GELSENKIRCHEN, June 21 (RIA Novosti) - Ukraine's Wladimir Klitschko defeated Ruslan Chagaev from Uzbekistan with a technical knockout on Saturday to retain his IBF and WBO heavyweight titles.

The referee stopped the fight before the start of the 10th round in front of 61,000 fans at Veltins Arena in Germany's Gelsenkirchen.

The much-anticipated June 20 fight in Germany between Klitschko and undisputed cruiserweight champion David Haye of Britain was canceled last week after the Londoner pulled out with a back injury he picked up in training.

Klitschko, although disappointed by Haye's injury, said he would nevertheless stick with the date for the fight and scheduled a bout with 30-year-old Chagaev.

Chagaev was scheduled to fight Russia's WBA Heavyweight Champion Nikolai Valuev on May 30 in Helsinki, but the bout was called off after the champion in recess was diagnosed with a mild form of Hepatitis B and was unable to meet the Finnish boxing federation's medical requirements.