Wladimir Klitschko beats Italian Francesco Pianeta in Germany

Wladimir Klitschko retained his WBA, IBF and WBO world heavyweight titles with a sixth-round stoppage victory against Italian Francesco Pianeta.

Ukraine's Klitschko, 37, was never troubled as he made the 14th defence of his belts in his second stint as champion.

Pianeta, who had been unbeaten in his previous 29 professional fights, was floored in the fourth and fifth rounds.

But Klitschko finished the contest in brutal style in the following round.

Klitschko has now won 60 of his 63 fights, with his last defeat coming in May 2004 when he suffered a fifth-round stoppage against American Lamon Brewster.

The 28-year-old Pianeta took a lot of punishment but stayed in the contest for six rounds, although he was hopelessly outclassed in Mannheim, Germany.

Klitschko, who could now fight unbeaten Russian Alexander Povetkin later this year, floored his opponent with a straight right hand in the fourth and then again a round later when he landed with a left hook.

But a powerful combination in the sixth sent Pianeta down again and, although he got up, referee Ernest Sharif stopped the contest.

Vitali Klitschko, Wladimir's brother, holds the WBC title.

Britain's David Haye - who lost to Wladimir in 2011 - was commentating at ringside and in a thinly veiled dig, Klitschko said: "I want to thank my opponent. There are a lot of challengers who talk a lot, but he got in the ring and fought bravely."

Pianeta recovered from testicular cancer in 2010 and Klitschko added: "After the battle he has had against cancer he deserves respect.

"He tried everything to hit me, if he had landed one his big punches, I wouldn't have got up."