Ukrainian boxing star Oleksandr Usyk delivered a stoppage win on his heavyweight debut on Saturday in Chicago, while Dmitry Bivol overpowered Lenin Castillo with a dominating attack to retain his WBA light heavyweight belt.
Usyk made the step up to boxing's biggest weight class after becoming the undisputed world cruiserweight champion. He has seen two changes in opponent after his original fight was cancelled when Carlos Takam got injured in training, while Saturday's original rival, Tyrone Spong, withdrew just weeks ago after a negative doping test.
Chazz Witherspoon answered the call to step in last minute and the American had no answers for Usyk, who broke down his opponent to the extent he quit on his stool before the seventh round.
Usyk (17-0-0) is looking to move up in the heavyweight division and fight some of the bigger names but he is going to have to prove himself against tougher opponents before he takes on the likes of Anthony Joshua, Tyson Fury or Deontay Wilder.
"I am ready to fight them. If they give it to me of course I am going to take it," he said.
Earlier, Bivol cruised to a unanimous decision, winning almost every round and knocking the challenger down in the sixth round of a slow paced fight in front of a crowd of 9,073 at the Wintrust Arena.
He defended his title for the seventh time winning by scores of 120-107 and 119-108 twice.
Bivol had no problem with Castillo, using combination punches to the body and head to wear the challenger down and score a knockdown in the middle of the fight.
Bivol connected with a right hand to the chin that sent Castillo staggering backwards then smiling awkwardly as he hit the canvas in the middle of the sixth.
Castillo was able to continue and take the fight to the distance but he spent most of time on the defensive and wasn't able to do much damage by counterpunching against Bivol, who improved to 17-0.
"I saw his fights before. He is really good at counter attacking. All five rounds before that, I tried to land that punch," Bivol said of the knockdown blow.
"I kept my belt and I still have a chance to fight for my dream and get another title," he said.
On the undercard, US fighter Patrick Day was in hospital after suffering a serious head injury following a brutal 10th round knockout by unbeaten Charles Conwell in a super welterweight bout.
American sports broadcaster ESPN reported late Saturday night that Day was in a coma after undergoing emergency brain surgery at a hospital.
