Wladimir Klitschko defeats Tony Thompson in six rounds

Wladimir Klitschko (right) lands a punch on Tony Thompson

Wladimir Klitschko retained his WBA, IBF and WBO heavyweight title belts by stopping American challenger Tony Thompson in the sixth round.

The Ukrainian world champion extended his unbeaten run to eight years by overcoming 40-year-old Thompson in Berne, Switzerland on Saturday.

Thompson never recovered from a big right hand from Klitschko near the end of the fifth round.

And the contest was over when Thompson hit the canvas again in the sixth.

It was 36-year-old Klitschko's 58th victory, 51 by KO, for only three defeats - and his 16th in a row.

Wladimir and his older brother Vitali have dominated the heavyweight division for so many years that they are now revisiting fighters from the past.

Thompson last met Wladimir Klitschko in 2008, when the American's challenge was ended in the 11th round.