Berlin John Ruiz lost the WBA heavyweight title Saturday night, dropping a disputed split decision to 7-foot Nikolay Valuev of Russia.
Valuev, who becomes the tallest and heaviest (323 pounds) champion of all time, won 116-113 and 116-114 on two judges' cards, with a third judge scoring the fight 114-114.
The crowd of 10,000 booed the decision.
"Boxing is the only sport where you can get robbed without a gun," Ruiz said. "My promoter Don King should do his job and get a rematch."
Ruiz manager Norman Stone had to be restrained in the ring when the announcement was made, and German promoter Wilfried Sauerland accused him of inciting the crowd, leading to the booing.
Each side admitted the fight was close after Valuev loosened up and won the middle rounds. He became the first Russian heavyweight champion.
"I'm always fighting a smaller man, and the crowd always supports the smaller man," the 32-year-old Valuev said of the crowd's jeers. "But I was perfectly sure at the end I had won. I had to wait 12 years for this, and now it has happened. It's fantastic."
Ruiz, who weighed 85 pounds less than Valuev at 238 and was 10 inches shorter, appeared to have the fight in hand, using a jab-and-grab tactic to slip in a few punches and then tie up Valuev.
Valuev began throwing combinations in the seventh round, adding to a left jab that landed from the opening round. In the ninth, Valuev even danced a bit. Valuev landed the only punch that did damage in the final round, hitting Ruiz on the chin with a straight left that wobbled the champion. Ruiz clinched his way to the end of the fight.
Ruiz's record fell to 42-6-1, while Valuev improved to 43-0 with one no-decision.
The American used the clinching moves that carried him through 11 title fights, with victories against Evander Holyfield and Andrew Golota.
In an earlier bout, Laila Ali stopped Sweden's Asa Sandell in the fifth round of a non-title bout, with her father, former heavyweight champion Muhammad Ali, watching.