BEIJING (AFP) - World champion Olga Kaniskina of Russia led from gun to tape to win the women's 20 kilometres walk gold medal at the Olympics on Thursday. In atrocious conditions on the course around the National Stadium, Kaniskina dominated the field and set an Olympic record of 1hr 26.31min.There were maiden track and field medals at these Games for Norway and Italy as Kjersti Platzer finished second, 0.36sec off the pace, with Elisa Riguado a further 0.05sec adrift.Defending champion Athanasia Tsoumeleka of Greece could only manage a ninth-placed finish in 1:27.54.In driving rain, Kaniskina broke away from the main field early on and slowly but surely built up a steady lead on her rivals which she never looked in danger of losing. "I didn't break the world record because of the weather," said the 23-year-old.She added, however, that the rain had not otherwise affected her performance on a carpeted circuit that ran alongside the Bird's Nest."It had no influence on me," she said of the heavy downpour. "It was better than a sunny and hot day. I didn't feel it was very slippery."I was in good condition. I think my regular training is the most important factor contributing to my victory."On the track, American Bryan Clay got his bid to unseat defending world and Olympic champion Roman Sebrle off to a cracking start in the first three events.Clay, the 2005 world champion, sped to a lead 10.44sec in the 100m, jumped a lead of 7.78m in the long jump, and set a personal best of 16.27m in the shot put, giving the American the overall lead on 2862pts, 292 ahead of Sebrle in 10th. The 33-year-old Sebrle of the Czech Republic, the reigning world record holder who also won silver in the 2000 Sydney Games, ran 11.21sec in the sprint, long jumped a best of 7.68m and putted 14.78m. The decathletes will compete later Thursday in the high jump and 400m. Their second day of competition, comprising the 110m hurdles, discus, pole vault, javelin and 1,500m, comes on Friday. Medalling events in Thursday's evening session include the men's 110m hurdles, 400m and triple jump, and the women's 200m and javelin final. There are also semi-finals in the men's 800m and women's 1500m ahead of Saturday's finals in each event, and men's and women's 4x100m relay teams race heats for Friday's finals. In the 400m final, reigning Olympic and two-time world champion Jeremy Wariner will face a showdown with top rival LaShawn Merritt. The 110m hurdles might have lost some of its lustre with the withdrawal through injury of defending Olympic and world champion Liu Xiang of China and American two-time Olympic silver medallist Terrence Trammell. But world record holder Dayron Robles of Cuba, American duo David Payne and David Oliver, and Frenchman Ladji Doucoure, all made it through. The women's 200m sees a trio of Americans - two-time 200m world champion Allyson Felix, Olympics debutant Marshevet Hooker and Muna Lee - face off against Jamaica's defending champion Veronica Campbell-Brown, Kerron Stewart and Sherone Simpson. Debbie Ferguson-McKenzie of the Bahamas and Cydonie Mothersill of the Cayman Islands complete the final line-up.