BERLIN - Undisputed world heavyweight champion Wladimir Klitschko retained his titles on Saturday with a fifth-round knock-out of Australian challenger Alex Leapai. Ukraine's Klitschko defended his WBA, IBF, WBO and IBO belts in Oberhausen and was in complete control of his 25th world title fight as he knocked-out Leapai after two minutes, five seconds of the fifth round."It wasn't easy, because my head was with my countrymen in Ukraine. What is going on in my home country is the concern of the whole world," said Klitschko, who landed 147 punches compared to Leapai's mere ten. "I hope that the politicians in my home country will find a peaceful solution, I am proud of my people."Klitschko picked up the 53rd knock-out of his career in his 62nd victory in the 65th fight of his career and had Leapai down three times before the referee stepped in. "You gave everything, respect," the champion said to Leapai. The 34-year-old Leapai had few answers and failed to live up to his pre-fight promises to knock Klitschko out. "I'm alright, I want to thank Wladimir for the opportunity, he showed why he's the champion," said the humbled Samoan-born challenger who suffered the fifth defeat of his career.Both fighters tipped the scales at 112kgs, but Klitschko had just over double the victories, compared to Leapai's 24 knock-outs in 30 wins, and had a 15cm height advantage. A heavy right from Klitschko put Leapai on the canvas midway through the first round and the Ukrainian champion was landing his shots at will in the second. Living up to his nickname "The Lionheart", Leapai soaked up the champions punches and kept looking -- in vain -- for a big hay-maker.But he took several direct hits in the face in the third with Klitschko using his height advantage to stay out of the Australian's reach. A sharp left hook caught Leapai in the fourth, but a heavy right-hand from Klitschko midway through the fifth caught Leapai flush on the side of the head and effectively ended the fight. Leapai was back on his feet by the count of seven, but Klitschko moved in and quickly had the Australian back on the canvas again as the referee waved the end of the fight.Klitschko suffered the last of his three defeats on April 10, 2004 to Lamon Brewster in Las Vegas and with the 38-year-old peerless in the division, he has said he wants to box on for another ten years. US legend Joe Louis' 12-year record for the longest reigning world heavyweight champion will fall if Klitschko is unbeaten for the next four years having won his first title in 2006.