The UFC Vegas 121 main event was one of the best fights of the year, but ended in scary fashion.

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.