BERLIN -- Wladimir Klitschko knocked out former sparring partner Tony Thompson in the 11th round to successfully defend his heavyweight titles Saturday.
Klitschko (51-3, 45 knockouts) turned boos to cheers, sending the American to the canvas with a right hand 1:38 into the 11th. He redeemed himself after an ugly 10th in which he pushed Thompson to the canvas and fell on him.
Klitschko's ninth straight win was tougher than expected, as he had to survive a second-round head-butt that left both fighters bleeding at the right eye.
"I'm still world champion, but it's about three titles now -- that means everybody that fights me is extra motivated," said Klitschko, who holds the IBF and WBO titles. "I haven't had a black eye for a long time, now I really look like a fighter."
His corner stemmed the cut, but his face was marked by the fight. His left eye was swollen after Thompson caught him with several good shots, especially a fifth-round right hook.
But Klitschko was ahead on the cards and caught Thompson in the sixth with two good rights to take control of the fight.
He tired after the seventh -- until he charged out in the 11th round and landed the knockout punch. That led the sellout crowd of 15,000 to chant "Klitschko, Klitschko" again.
"They were both tired, but Wladimir has experience now, then he came back with a second wind," Klitschko trainer Emanuel Steward said. "I said Thompson would be one of the most difficult fights we will have."
The fight came after Klitschko decisioned Sultan Ibragimov at Madison Square Garden in February, gaining him the WBO title but no winning many fans with a lackluster performance.
Thompson (31-2, 19 KOs) was a WBO mandatory fight for Klitschko. He served as Klitschko's sparring partner before one of the Ukrainian's worst losses, a two-round stoppage by Corrie Sanders in 2003.
Thompson's 27-fight unbeaten streak dating to 2000 was snapped. When Klitschko fell over him, Thompson's knee was hurt. However, the American said that was temporary and didn't lead to the knockout.
"I was fatigued, I thought he was fatigued too," he said. "He did what a great champion did, he took advantage when I was vulnerable. The only thing that hurts on me is my heart -- for losing."
Next up for Klitschko is likely Alexander Povetkin, the IBF mandatory challenger, if the Russian can beat Taurus Sylkes next Saturday. If not, cruiserweight champion David Haye -- who said he wants to fight Klitschko -- was in the audience for the bout.
"There's a line waiting to fight me," Klitschko said. "We will try to decide, maybe in a couple of weeks."
The 36-year-old Thompson gave the Klitchko problems with his size. Thompson is two inches shorter than the 6-foot-7 Ukrainian.
"He made it difficult," Klitschko said. "I didn't have the rhythm at the start, but the jab got better each round."
Thompson failed in his goal to make a name for himself back home in the United States with a Klitschko win. His promoter, Dan Goosen, promised to line him up some other big money fights after the better-than-expected performance.
Klitschko, who started his career in Hamburg, fought in the city for the first time in eight years.
On the undercard, American Jonathan Banks (19-0-0, 14 knockouts) won a decision against Italy's Vincenzo Rossitto (36-5-4, 22 knockouts) to claim the vacant IBO cruiserweight title.