It's been a couple of days since UFC 293 and it's still shocking and hard to process — Sean Strickland is the middleweight champion of the world. That said, it's not exactly the biggest upset of all time. From an odds perspective, Holly Holm's knockout win over Ronda Rousey in 2015 still stands at the summit.

However, it was certainly the biggest upset in a middleweight title fight and follows a recurring theme in 2023 where there have been a number of shocking wins for the underdog. Is Sean Strickland's win over Israel Adesanya the biggest? Let's take a look at the five biggest upsets in 2023.

5. Brendan Allen vs. Andre Muniz – UFC Vegas 70

Andre Muniz was on a nine-fight winning streak going into his Fight Night headliner with Brendan Allen. The Brazilian — known for his submissions — was also 5-0 in the UFC with wins over Jacare Souza and Uriah Hall. While Allen was on a three-fight winning streak at the time, the confidence was clearly with Muniz who closed as high as a -250 favorite.

What followed was Allen not only upsetting the odds to defeat Muniz — he also did it with a submission as well.

4. Sean O'Malley vs. Aljamain Sterling – UFC 292

It might seem odd to have this fight on this list, but it's a weird fight as a whole. Sterling was a big favorite going into the fight and just about every top MMA fighter was picking him to emerge victorious. At the same time, an O'Malley win — especially by knockout — wouldn't have surprised anyone. The only factor was whether O'Malley could keep the fight on the feet as if Sterling took him down, the result was all but inevitable.

Sterling closed as a -275 favorite, but was unable to get O'Malley down thanks in part to the latter's footwork and movement. In the end, O'Malley caught Sterling with a counter right as he was closing in and the rest is history.

3. Alexa Grasso vs. Valentina Shevchenko – UFC 285

Funnily enough, the rematch between Alexa Grasso and Valentina Shevchenko takes place Saturday night at Noche UFC. It's a rematch because Grasso shocked the world by submitting Shevchenko in the fourth round of their women's flyweight title fight back in March. It was Shevchenko's first defeat since 2017 as well as her first at 125 pounds.

Just how big a favorite was Shevchenko going into the first fight? She closed as a -1200 favorite (Grasso was as high as a +750 underdog) and even going into the rematch, she remains a solid favorite to further showcase how big an upset this was. To make matters worse, Shevchenko was winning the majority of the first fight. It's one of the reasons “Bullet” has a fiery mindset going into their second fight.

2. Dricus du Plessis vs. Robert Whittaker – UFC 290

While Dricus Du Plessis wasn't as big an underdog as Grasso nor was Robert Whitaker as big a favorite as Shevchenko, if you asked any MMA fan what would be more shocking, the chances are they'd say Du Plessis beating Whittaker. It just seemed next to impossible given how well-rounded Whittaker was while Du Plessis was just a brawler who had yet to fight any true high-level middleweight. He may still be undefeated in the UFC, but he had plenty of clumsy moments that made people think the fight was a foregone conclusion.

And yet, Du Plessis — who had notably fixed his breathing problems after undergoing surgery — looked a new fighter. He took Whittaker down and ground and pounded him in the first round before dropping him in the second and going on to get the finish. Whittaker claimed afterward he simply had an off night, but even then, it's a result that still remains hard to digest even three months on.

1. Sean Strickland vs. Israel Adesanya – UFC 293

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In the end, Strickland's win over Adesanya will likely remain the biggest upset of 2023. For starters, there was very little enthusiasm for the fight because of how much Adesanya was favored to win. The general belief was Strickland was a tailor-made matchup for “The Last Stylebender” who would either get the finish or a comprehensive decision victory. Strickland wasn't a knockout threat while he didn't proactively wrestle or grapple either.

And yet, Strickland not only defeated Adesanya. He outclassed him over five rounds to get the unanimous decision win — all without grappling whatsoever. He even dropped Adesanya with a right hand towards the end of the first round. Upsets usually come in the form of a finish, but Strickland was able to nullify Adesanya completely with all three judges scoring it 49-46 in his favor. There was no chance of any robbery either because Adesanya just couldn't land on Strickland.

There are still a couple of months left in the year, but it's hard to see this result getting topped.