Fedor-Minotauro I
Minotauro was viewed as the best fighter in MMA to most and the best HW we'd seen in MMA, was practically undefeated, avenged his only "loss" (a robbery decision) to Hendo decisively. He was at his peak, and had the most dangerous guard in the sport. Fedor went into it and delivered an absolutely dominant performance. Some of the most devastating g&p ever, masterclass in submission escapes. Minotauro landed 3 significant strikes throughout 20 minutes and had all his TDs stuffed. After this fight, he didn't lose to anyone not named Fedor for many years either.
Penn-Hughes I
Hughes was a top 3 P4P guy alongside Fedor and Wand, the most dominant fighter in the UFC for sure and best WW in MMA, by far. He still remains the 2nd greatest WW ever, and Penn moved up a division and strangled him inside a round. Hughes went 19-1 in a period from 2001-2006 with this being his lone loss (which he avenged, and also stopped GSP in that 20 fight span). Even up until 2008, the loss to Penn and 2 losses to GSP were his only defeats in his prime.
Dillashaw-Barao I
Barao was unanimous top 3 P4P alongside Aldo and Bones, kind of similar dynamic to Merab being top 3 P4P alongside Topuria and Makhachev. Dana infamously called him P4P #1 leading up to the fight. People were starting to say he might be the best BW we've seen in MMA, especially after the Faber rematch. He hadn't lost in over 9 years, 32 fight win streak. Then Dillashaw just puts on one of the most spectacular, inimitable performances ever.
Whittaker-Romero I
Romero was essentially the best MW in MMA to most, undefeated at the weight and it was hard to see him lose. This might have been the best overall athlete we've seen in MMA really develop a high level, cohesive game with Olympic level wrestling, one of the most credentialed, dominant wrestlers to ever transition. Whittaker showed one of the greatest displays of TDD ever and also took the fight to Yoel and hustled 3 rounds down 0-2 after suffering a torn MCL in the 1st round. I think Romero was better equipped for the rematch, and deserved a draw at least, but by then, his wrestling had started to slip, or he became more of a striker. He also missed weight.
Volkanovski-Holloway III
Complete shutout of one of the greatest fighters ever. 3rd time was the charm though since many thought Max won the rematch, but Volk left no doubts after this one. He didn't have to attempt a single TD in this fight either, which was unexpected.
Aldo-Edgar
Either one honestly, but the rematch was probably more dominant and Frankie was more acclimated to 145-lbs by then, wasn't his first rodeo like their fight fight. One of the P4P GOATs in the heart of his prime and Aldo decisively beat him and really neutralized his game for many rounds, which was unprecedented. In his prime, Frankie was never decisively beaten outside of the Aldo fights. Maynard beat him clean the 1st fight, but he wasn't in his prime yet. Then his series with Penn, Maynard and Bendo were all highly competitive, close fights. The Aldo fights were competitive in minutes, but overall Aldo ran away with the fights.
Yan-Dvalishvili
Honestly, you can put both of the fights here. Yan's win is fresher in our minds and warrants the praise it gets, but Merab threw 400 strikes and shot 49 TDs in that fight to a 50-45 win. The Yan injury is something to consider, but the sheer output and pace by Merab that fight is something we might not ever see in MMA. Yan, despite the claims of being compromised, still showed great defense throughout the fight (offense is another story), but Merab bamboozled him with his feints and overwhelmed him. Merab also hurt and injured him with a calf kick in round 1, which really compromised Yan (he checked a similar kick in the rematch, and Merab barely threw it afterwards).
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In hindsight, Khabib-RDA might need to be up there since he was already at Kings MMA when they fought and that was his sole loss there before the Alvarez loss (where he had a really bad weight-cut) and Khabib shut him out. RDA's performance against Pettis is also up there. Pettis was as dangerous as any LW we'd seen in that run, having stopped Lauzon, Cerrone, Bendo and Giblert with ease. It was as thorough an outclassing as we've seen at the elite level, all phases of MMA and dominating every round against a top P4P fighter, an ATG LW at his peak and one of the most devastating finishers ever.