World heavyweight champion Wladimir Klitschko retained his titles with an easy victory over Jean-Marc Mormeck.

A 50th knockout of his career enabled the 35-year-old to beat the French challenger in the fourth round in Dusseldorf.

Former world cruiserweight champion Mormeck, who floored David Haye in losing his world cruiserweight titles to the Englishman in 2007, was no match for the IBF, IBO, WBO and WBA title-holder.

The fight, originally scheduled for last December but postponed because Klitschko had a kidney stone removed in the same month, went as expected.

The first round was a one-sided affair with Mormeck's approach seemingly to suppress the Ukrainian.

The Frenchman was soon on the back foot in the second round and after his legs had wobbled under the power of a Klitschko right-hander he found himself on the floor after another.

To his credit Mormeck got up and saw out the end of the round and held his own in a scrappy third, in which Klitschko failed to press home his two-stone weight advantage.

However, the contest was ended a little more than a minute into the fourth with a fearsome right-left combination sending Mormeck, who will be 40 in three months' time, to the floor.

Puerto Rican referee Luis Pabon counted out the challenger, who had fought just three times since losing to Haye - leaving Klitschko to celebrate a 57th career win.