On Saturday night, Barcelos took on Raul Rosas Jr. in the main event of UFC Vegas 121. It was Barcelos' first UFC main event, and it was going extremely well for him, with Barcelos up on all three judges' scorecards heading into the fifth round. But then, disaster struck.

In the fifth round, Rosas complete a takedown on Barcelos against the fence, and then after posturing up and landing a shot, Rosas stepped off the unmoving Barcelos, securing a KO win. Barcelos was immediately seen to by medical officials but remained on the ground for a long time, with the production team not even showing him. Even after multiple replays, it's still unclear exactly what happened to Barcelos, who was stretchered out of the APEX and the MMA community has him in their thoughts, reacting to the terrifying scene.

Raul Rosas Jr. and Raoni Barcelos competed in their first UFC headliners on Saturday at the Meta APEX. After four wild rounds, the fifth round is when the fight stopped after Rosas landed a takedown, and Barcelos went unconscious and limp.

Check out the way the fight ended below.

The fight was action packed through the first two rounds with Rosas coming out guns blazing early, throwing everything but the kitchen sink at his veteran opponent. Barcelos began to close the cap, and used that momentum in the second round — landing nearly 60 significant strikes in the round as Rosas visibly began to slow down.

Round 3 was back and forth with Barcelos getting a nasty foot sweep takedown and dominant back position. Rosas was able to sweep, get top control, and land some good ground and pound. But Barcelos got back up and continued to pile up damage and fatigue numbers on the Rosas side.

In the fourth, it was all Barcelos, delivering a pillar-to-post beating on the feet and on the ground to Rosas, nearly finishing the fight on multiple occasions. But in the fifth, Rosas went for it knowing he needed a finish, then landed the takedown that ended the fight.

With multiple replays, it was hard to see what actually knocked Barcelos out, but he was stretchered out of the APEX.

After the win, Rosas put over Barcelos for his toughness, called for a bonus, and asked for the top-seven opponent.

Perez and Dumont competed in a rivalry matchup in the co-main event of UFC Vegas 121. After a matchup that delivered up and down action, as the final horn sounded, it took multiple members of security to step in and keep the two ladies apart before Perez was announced the surprising unanimous decision winner.

Check out the scene after the bout ended below.

Perez set the tone in the first round winning the striking battle — although it was competitive — but a takedown late in the round sealed off a clear-cut round for Perez. Dumont's aggression came out a bit more in Round 2, landing an early takedown, but Perez was able to get back to her feet, which is where the majority of the round was contested. Both women got a bit more tepid as the stanza commenced, although Dumont landed the most significant punch of the round in the final 90 or so seconds. Dumont began taunting and talking to Perez, and almost ate a spinning back fist for her troubles.

The third round looked quite similar to the second, although Perez finally got a hold of Dumont and pushed her against the fence, while landing a brutal knee to the body. Perez landed a big left hand at the horn, and Dumont continued taunting her opponent until security intervened.

The result was a 29-28 on all three scorecards for Perez, which left Dumont stunned, and then the fight almost re-started again after Perez did her dance.

“She treated me like a prostitute, what do you want me to say?,†Perez said in the post-fight interview.