When two warriors enter a cage to battle for physical supremacy, why do we assume the odds are so heavily packed in favor of one person? Yes there is skill and experience that comes into the equation, but if the sport of MMA has proven anything, it is that upsets can happen at the drop of a hat. One slip, one punch that just misses the mark is all that can separate a win from a crushing defeat and a bloodied face.

Within the last 12 months, the Ultimate Fighting Championship has been blessed with some epic encounters and turn ups for the books. Conor McGregor, a man who appeared to be above the fray and riding the crest of a popularity wave had to tap out against a ringer who had stepped in at the last minute. All of a sudden the cocky Irishman is left licking his wounds and biding his time until a rematch can be finalized.

Down under last year, Holly Holm illustrated what a bit of discipline and tenacity can accomplish. Coming into the huge contest in Melbourne, Australia had a serious dose of Ronda Rousey fever, buying into the mythology and celebrity she had garnered through years of dominating her opponents and shining outside the arena. Fast forward to a series of lightning fast punches and the spell was broken. It shell-shocked viewers around the world and put weight behind the notion that the UFC is one of the best sports when looking for upsets.

Perhaps these fights have played a serious role in the rise of the UFC, perhaps they are just part of the narrative of the brutality and rawness that gives it the widespread appeal. Whatever the cause, the Ultimate Fighting Championship has won over a lot of new fans by creating icons and champions from all types of backgrounds from every corner of the world. Until we see what 2016 has in store for us, let’s recap the 20 greatest upsets in UFC history.

20 20. Rafael dos Anjos vs. Anthony Pettis

The odds were stacked in the favor of Anthony Pettis fighting for the Lightweight Championship in UFC 185. His take-down of Gilbert Melendez came off the back of a significant lay off and with the governing body granting him his request to come back into the fol,. Rafael dos Anjos made him reconsider that decision as he dealt “Showtime” a 25-minute beating. An early left hook broke his orbital bone in the first round and from that point on, Pettis had gone from comfortable favorite to punching bag.

19 19. Paulo Thiago vs. Josh Koscheck

Josh Koscheck was displeased with the result to say the least, unable to compute how the referee could have handed down such a decision: “How the f**k?” Paulo Thiago was thought to be nothing more than practice material for Koscheck in UFC 95, despite the fact he had a 10-0 record. A huge right uppercut from the Brazilian put Koscheck on his backside and transformed his image in the sport. “I got hit,” admitted the fallen fighter. “But my f**king eyes were open.” Not open well enough to see that uppercut though.

18 18. Royce Gracie vs. Gerard Gordeau 

Every superhero needs a good origin story, just like every combat sport needs a fighter to embark on that first mission into the unknown. UFC 1 way back in 1993 was uncharted territory for all concerned and world karateka champion Gerard Gordeau was heavily favored to go the distance. But standing in his way was Royce Gracie, a Brazilian jiu-jitsu fighter who looked just as unthreatening as he was unconventional. Dressed in full white robe-type clothing, he engaged Gordeau in a choke around the neck to force a tap out and with it, victory. The inaugural UFC winner, of course, had to come from a major upset against all odds.

17 17. Chuck Liddell vs. Keith Jardine

The bounce-back fight for a champion and face of the UFC brand that should have been, but never was. Yes Keith Jardine’s split decision takedown of Chuck Liddell was beautiful in it’s brutality, seeing the official decline of “The Iceman” through vicious blows and kicks that would chip away at most fighters. Jardine’s tactics were to unsettle the veteran until the pressure became too much and even though he recovered to beat Wanderlei Silva following UFC 76, this encounter demonstrated how far Liddell had fallen in the UFC pecking order.

16 16. Pete Williams vs. Mark Coleman 

In a fight that sounded more like an organizing party for fantasy baseball than a battle in the cage, Williams’ head kick knockout of Mark Coleman in the second round of UFC 17 demonstrated how quickly the pecking order can shift. Coleman was coming off the back of a Heavyweight title defeat and a matchup with Pete Williams was expected to be a nice little welcome back into the victory column. And while Coleman looked solid enough through his tough wrestling approach, his “Hammer” nickname came back to bite him, as he was nailed with a swift roundhouse to defy those that wrote Williams off.

15 15. Eddie Yagin vs. Mark Hominick

The wordsmiths described it as a “bloody slugfest” and given the appearances of both gentlemen at the conclusion of this UFC 145 throw down, they were right. Featherweights Mark Hominick and Eddie Yagin fought out a bitter split-decision with Yagin putting the favorite Hominick on the canvas, but rather than ride out his upset, he had to cop a barrage of hits to narrowly win over the judges 29-28, 28-29 and 29-28 to edge the narrowest of wins possible. It was Yagin’s first ever success in the octagon and saw Hominick’s decline officially bottom out with his three straight defeat.

14 14. Randy Couture vs. Chuck Liddell

Heading into UFC 43, it seemed like no could stop Chuck Liddell. He had won 10 consecutive bouts, including wins over Vitor Belfort and Renato Sobral while Randy Couture was coming off defeats by the hands of Josh Barnett and Ricco Rodriguez. With Tito Ortiz exploring other fights at the time, Randy “The Natural” Couture melted “The Iceman” in the 3rd round after a barrage of punches forced the referee’s hand. It was the start of Randy’s rise in the Light Heavyweight division and the beginning of a trio of encounters.

13 13. Chris Weidman vs. Anderson Silva  

Chris “The All-American” Weidman was quietly going about his business leading into UFC 162 in 2013, only to be given a shot at powerhouse fighter Anderson Silva. The Brazilian hadn’t tasted defeat since 2006 and when Weidman landed one devastating left hook in the opening minute of round two, another quickly followed and as the referee stopped proceedings after a flurry of punches, the UFC Middleweight Champion had changed address. Weidman would prove that win was no fluke, doing the deed over Silva six months later just after Christmas.

12 12. Jens Pulver vs. B.J. Penn

Jens Pulver pulverized B.J. Penn into submission during UFC 46 way back in 2002, giving hope to the little lLghtweights who one day aspire to lift their game for the big occasion. The man they called “Lil’ Evil” barely made a false move in the 5 rounds to outclass and outmaneuver a fighter most expected to do the job in quick time. It was a major setback for Penn but it helped put Pulver on the map, as well as his low-center-of-gravity style to the forefront. He showed that size isn’t always the best ingredient to success.

11 11. Gabriel Gonzaga vs. Mirko CroCop

Mirko “Cro Cop” Filipovic looked like something carved out of a Croatian factory, having the chiseled jawline and six pack abs that made him appear like a machine. Before UFC 70, Mirko had finished off Eddie Sanchez, Wanderlei Silva and Josh Barnett heading into his fight with the “Gatekeeper” Gabriel Gonzaga. But it would be Gonzaga who ironically used CroCop’s iconic roundhouse kick technique to put the Croat to the canvas. Filipovic settled the score eight years later and retired knowing that upset wouldn’t haunt him for the rest of his days.

10 10. Randy Couture vs. Tim Sylvia

Every time he walked away, somehow he pulled himself back in. Randy Couture already had two heavyweight crowns before UFC 68 and at 43 had nothing left to prove to anyone, except himself. “Not bad for an old man,” is how he categorized the five round beating he dished out to the 43-pound superior Tim Sylvia, coming out retirement in 2007 to destroy a man who had won his last six fights and at 6 ft. 8 seemed a monster that could not be slain. Couture wasn’t an old dog who needed to be taught new tricks,and this proved it.

9 9. Frankie Edgar vs. B.J. Penn

“The Prodigy” B.J. Penn was given a lesson in boxing skills during UFC 112 in Abu Dhabi in 2010. Dropping down to Lightweight, the veteran was expected to make light work of Frankie Edgar, but the fight did not go according to script with the New Jersey boy roughing up the highly fancied Penn from start to finish to earn a decision in his favor that was more than warranted. The onslaught of knuckles unleashed on Penn outlined how falling down a weight division doesn’t immediately make you a favorite.

8 8. Thiago Santos vs. Ronny Markes

53 seconds is all it took for Thiago Santos to lay on the body kicks and punches to Ronny Markes. One particular blow to the liver meant the final preliminary-card contest in Brazil for UFC Fight Night 38 would be a short one, making a mockery of the more experienced Markes. Santos’ lanky and languid style wasn’t supposed to deal as much damage to Markes, yet the fighter explained in the aftermath, “He hit me right in the (solar) plexus. I couldn’t breathe. I couldn’t move my abdomen.” A flurry of shins to that part of the body will slow anyone down!

7 7. Fabricio Werdum vs. Cain Velasquez

UFC 188 bared witness to Fabricio Werdum taking out hometown hero Cain Velasquez on enemy territory, providing a tearful celebration amass a crowd of Mexicans disappointed their man couldn’t fulfill the hopes of the locals. Some thought Velasquez was a contender to be one of the UFC’s greatest ever heavyweights but a severe choke in round three was just insult added to injury on a night that few saw coming.

6 6. Forrest Griffin vs. Mauricio Rua 

Forrest Griffin’s infamous reaction to his victory over Mauricio ‘Shogun’ Rua to this day remains one of the most iconic images in UFC history. The contestant from Ultimate Fighter came into UFC 76 with a notable win over Stephan Bonnar, but not much else. Rua made a habit of crushing opponents until in the 3rd round against Griffin, he succumbed to a rear-choke that gave him his first taste of defeat. Rua won the rematch in UFC 134 in a first round hammering, yet the first showdown was the one to remember for Griffin fans.

5 5. B.J. Penn vs. Matt Hughes 

It might be the closet thing to a UFC version of Apollo Creed coming back to help Rocky Balboa. B.J. Penn vs. Matt Hughes gave the sport three epic encounters, all occurring off the back of an initial upset in 2004 that made everyone sit up and take notice. Coming up in weight division to Welterweight, Penn fought a Matt Hughes who had won 13 consecutive fights and was expected to push over his lighter opponent with ease. Yet the first round choke submission altered the landscape and although Hughes avenged his loss, the pair joined forces to train Penn in 2011. Penn’s UFC 123 KO of Hughes to settle the score 2-1 is the last victory of his career.

4 4. T.J. Dillashaw vs. Renan Barao 

Renan Barao reigned supreme as a Bantamweight UFC fighter. A nine-year unbeaten record is what he brought into his encounter with the unheralded T.J. Dillashaw, unbeaten in 33 fights to be close to unbeatable for a 34th straight. But his 2014 fight flipped the script, seeing Dillashaw land punch, after punch, after punch to defy those that couldn’t believe he was given the chance to stand in for the injured Raphael Assuncao. Through five rounds he gave the Brazilian a beating of a lifetime to laugh in the face of his 9-to-1 underdog status.

3 3. Nate Diaz vs. Conor McGregor

Most fresh in the memory is Nate Diaz’s stunning takedown of Irish firebrand Conor McGregor, a man who had strutted and brazenly talked down his opponent on talk shows and press conferences with the abandon of a man above the sport. But if the UFC has taught us anything down the years, it is not to cash in your chips until the win is guaranteed. Diaz stepped in weeks in advance for the injured Rafael dos Anjos, before trading blows with McGregor and as the canvas become a darker shade of red in the second round, Diaz pinned McGregor with a choke he couldn’t escape. The Irishman was criticized for fighting above his original weight in UFC 196 but wants to do it all over again. Crazy man.

2 2. Matt Serra vs. Georges St-Pierre

If there is any fight in history, in UFC, boxing or otherwise, that demonstrated the power and devastation one punch can cause then the Matt Serra victory over Georges St-Pierre was it. The UFC 69 bout back in 2007 pitted a seemingly unbeatable man in St-Pierre against a rough-around-the-edges combatant and from the surface it seemed a one-sided affair. The Canadian notched wins over heralded fighters like Sean Sherk, B.J. Penn and Matt Hughes leading in, but one single blow in round one changed everything.

1 1. Holly Holm vs. Ronda Rousey

Those observers at pubs and clubs who previously had no idea, interest or dog in this fight suddenly understood why the sport of UFC had the world watching. It wasn’t even the fact that Holm was a 22-to-1 underdog heading into the UFC 193 encounter in Melbourne or the fact UFC president Dana White had dubbed Rousey the female Mike Tyson of the sport. It was what it represented – an unheralded but polished fighter putting a cherished champion to the canvas with a flurry of punches and roundhouse kick to the neck. Comparisons were made with Buster Douglas, transforming a never-was to a once-in-a-lifetime sporting moment. It transcended the UFC and rarely can any sport say that that's happened.