BERN, Switzerland -- Wladimir Klitschko stopped Tony Thompson in the sixth round to retain his WBA, IBF and WBO heavyweight title belts Saturday night.

The 36-year-old champion Klitschko, 58-3 with 51 knockouts, floored Thompson with a big right hand near the end of the fifth round at Stade de Suisse, and the 40-year-old American never recovered.

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The Ukrainian champion dropped Thompson again in the sixth, and referee Sam Williams gave the challenger a standing count before stopping the fight.

In 2008, Klitschko stopped Thompson in the 11th round.

Thompson, who was the mandatory challenger nominated by the IBF, dropped to 36-3.