Brazil's Alex Pereira roared back from a poor start to knock out Khalil Rountree Jr. and retain his light heavyweight title at UFC 307 on Saturday, while in the co-main event, Juliana Pena beat Raquel Pennington to reclaim the women's bantamweight crown.

American Rountree's lightning-fast striking posed a problem in the early going for Pereira and a right-hand counter from an awkward angle briefly dropped the Brazilian in the second round.

Wary of his opponent's power, Pereira struggled to land telling combinations but the tide began to turn in the third round as he targeted Rountree's lead leg with calf kicks to slow him down, and a body kick and a stiff jab early in the fourth signaled the beginning of the end.

Rountree did his best to stand his ground but Pereira was merciless, stalking his opponent around the cage and landing thunderous punches to leave blood streaming from several cuts. Two heavy body shots and an uppercut finally broke Rountree's resistance late in the round and the fight was stopped.

A former champ at middleweight, Pereira has hinted at a move to heavyweight to try to secure a third belt, but his relationship with champion Dricus Du Plessis means he will not be doing so just yet.

"He's a training partner of mine, I don't want to get in his way. I can move up to heavyweight, but this division is great, I feel great with this weight cut and this is where I'm at," he said in a post-fight interview.

In the evening's co-main event, Pena, who defeated Brazil's Amanda Nunes to win the bantamweight belt in December 2021 only to lose the rematch the following July, was taken the distance by Pennington in their five-round title match-up.

Pennington became champion in January of this year when she defeated Mayra Bueno Silva and thought she had done enough to retain her title here, but two of the judges gave the fight to her opponent, resulting in a split decision victory for Pena.