Champion Wladimir Klitschko KO'd challenger Alex Leapaiin the fifth round to retain his three heavyweight belts on Saturday.Klitschko recorded his 53rd KO in 62 wins, with three defeats. Leapai dropped to 30-5, with three draws.In his 25th world championship fight, Klitschko retained his WBA, IBF and WBO heavyweight belts, as well as the lineal title.Leapai was the first Australian