The American caught Kovalev with a big right hand and followed it with a series of shots to the body. Kovalev sat on the ring rope, and the referee signaled an end to the bout at 2:29 of the eighth round.
So they meet again on Saturday night (Sunday morning, Singapore time) in Las Vegas as Kovalev tries to wrest back the World Boxing Association (WBA), World Boxing Organisation (WBO) and International Boxing Federation (IBF) titles he surrendered in his first professional setback.
Both fighters swing and miss.
Last November's title fight between Andre Ward and Sergey Kovalev was one of the most controversial in boxing a year ago. But although Ward earned the victory, it did not come without a cloud of controversy, with many scorers claiming that Kovalev should have in fact been the victor. "I felt so much presser for the fight - my first fight on HBO Pay-Per-View - that I just trained too hard". "He is a great fighter, and when you fight great fighters, you have to raise your game".
Fans on social media called the stoppage premature, Kovalev echoed that sentiment in his post-fight comments, but with little energy left Ward would've found a way to stop him in the remaining rounds.
I am looking forward to making a statement in this fight, and removing any doubt that may be out there, Ward said.
Only Kovalev had fought at Mandalay Bay before during his career. Kovalev had success with his jab and the occasional right hand, while Ward looked to slip underneath his lead and attack the body at every opportunity.
The light heavyweight champ told Complex on June 12, "The only thing I've noticed about him [Kovalev] that's different since the fight ended is just the lack of mental toughness that this guy has". I didn't feel that hurt.
After seven rounds, judge Steve Weisfeld had Kovalev ahead 68-65 while judges Glenn Feldman and Dave Moretti had Ward ahead 67-66.
That likely explains why Kovalev stormed off stage before the end of Thursday's final press conference, declining to participate in interviews and the traditional staredown photo shoot.
"I don't know, I can't explain it", Kovalev said.
"I think it was plain to see that I broke him mentally and physically". I got exhausted, but I still wanted to fight.
"That's really what got me in my hole: the start".
When asked what's next for the undefeated Ward, he said he will possibly move to cruiserweight, or heavyweight.
There was genuine dislike between the two fighters, born largely out of their first fight.
Ward stopped Kovalev in the eighth. Ward, who caused a brief pause in the fight in the second round when he hit Kovalev below the belt, was never warned after that by Weeks for low blows. Ward came on strong in the second half of that fight after Kovalev knocked him down in the second round.
Ward not letting Kovalev get the big shots off. Kovalev connects to the face.
The victory was disputed as television replays showed Rigondeaux landed a left hand after the round-ending bell had rang. He also landed 3 punches while holding Flores' head from behind just before the knockout.