Junior dos Santos' inability to capitalize off of stuffed takedowns and passiveness when clinching were the biggest factors in his loss.
The first fight between Junior dos Santos and Cain Velasquez remains an oddity. I have always felt that JDS's knockout of Velasquez is, perhaps, one of the biggest flukes in MMA history.
That isn't to say Junior dos Santos is bad, or that he didn't deserve to be champion or even that I expected him to lose. But come on. If you run that fight through a computer 100 times, would you see “Cigano” score a victory like that more than once?
I, personally, don't think so.
The UFC 155 bout is what most expected the first fight to look like (though I doubt everyone expected such a thorough beatdown). Everyone believed Velasquez was going to use his strong wrestling to wear down dos Santos and use his freakish gas tank to keep a pace that few over 170 lbs are capable of maintaining. Dos Santos, by the way, checked in at 239 lbs.
The first round was, by far, the worst for dos Santos. Velasquez landed big punches and poured on ground-and-pound from bell to bell. Dos Santos, immediately after standing, was visibly woozy and tired from the beating he had received. Only four more rounds to go, though, right?
At the very beginning of the second round, we saw the first sign that there was no coming back for dos Santos in the form of a wild, telegraphed haymaker of an uppercut. That sort of ugly, home-run-style swing is not something we see out of highly technical strikers at the peak of their games. That punch was something we would see from Roy Nelson after ten minutes of being punched in the face, or Chris Leben at any point in a fight.
It was obvious at that point that the initial barrage had taken a lot of wind out of the champ's sails. He was sluggish, both in terms of his footwork and hand speed. Worse yet, he was painfully flat-footed. Those two factors combined made it impossible for dos Santos to effectively avoid the forceful takedowns of Cain Velasquez.
The second and third rounds were just more takedowns, more punches to the head and more abuse for dos Santos. In the fourth and fifth rounds, he would show signs of life by upping his movement, anticipating Cain's shots and just generally being sprier on his feet. That said, even if he did muster up a strong effort, that was still not nearly enough for the champ to come out on top.
It's tough to read too much into dos Santos' performance here. The two things dos Santos needs to work on, obviously, would be his sprawls and his clinch game. Dos Santos simply could not resist being taken down by Velasquez any time he closed the distance.
Dos Santos was not able to punish Velasquez when his takedowns weren't clean, and was badly out-muscled and outworked when against the cage. Velasquez had very little fear about getting punished when getting close and, because of that, never felt any repercussions for failed takedowns or less-than-perfect exchanges while clinched.
How much of this was his mashed potato brain from the first round beating, and how much of this was an actual weakness in the game of JDS is impossible to say at this point.
Dos Santos still owns some of the best boxing in MMA as a whole, and still has as much one-punch knockout power as anybody in the sport. Some are criticizing the now-former champ's cardio. While he most certainly looked sluggish and tired in the second and third rounds, the brutal beating he took from Cain was probably the real culprit more so than inadequate preparation (his relative activity in the fourth and fifth rounds would seem to agree).
With that in mind, Junior dos Santos still has the tools to beat Cain Velasquez if the two end up fighting each other again (which could be fairly soon). If dos Santos doesn't take such a harsh beating in the first round, it is possible he will have enough gas in the tank to win the middle rounds of the fight to keep things, at the very least, interesting en route to a decision.
Because of that, once again, the only real factor here was that dos Santos just needs to work on punishing grapplers when they attempt takedowns. If he can find a way to follow up on the flopping that Velasquez was doing at the start of the first round, we could easily see dos Santos wearing a belt again in no time.