Vitali Klitschko retained his WBC heavyweight ***le by knocking out Cuba's former Olympic champion Odlanier Solis in the first round in Cologne.
The Ukrainian, 39, caught his opponent with a decent shot towards the end of the round and Solis appeared to suffer a knee injury as he went down.
Klitschko was initially furious that Solis was not carrying on and 19,000 watching fans also voiced their anger.
But the referee ruled that the Cuban was unable to continue the fight.
Solis, 30, went into the ring with a perfect 17-0 pro record (12 by KO), and began confidently enough.
Both men were still getting the measure of each other when Klitschko landed a solid right on the side of Solis's head.
The punch almost seemed to have a delayed reaction as Solis crumpled backwards, and he was initially unable to rise, clutching his right knee.
"I'm so sorry for everyone who wanted to see a long fight, but I hit him pretty hard," said Klitschko.
With younger brother Wladimir, the IBF and WBO heavyweight champion in Vitali's corner, the fight was watched at ringside by Adam Booth, the trainer-manager of WBA ***le holder David Haye.
Britain's Haye is set to fight Wladimir in a unification bout this summer, and could also face Vitali at some stage.
But after the latest win for Vitali (42-2, 39 KOs), Wladimir said that Haye would be relieved to be facing him and not his older sibling.
"Haye will be glad to be fighting the younger, weaker brother," he joked.
