American Brian Clay clung to an 88-point lead after Thursday's opening day of the decathlon with world and Olympic champion Roman Sebrle of the Czech Republic in tears after struggling home fifth.
Clay, the 2004 Olympic runner-up, stood on 4521 points after five events with Andrei Krauchanka of Belarus second on 4453 with another American, Trey Hardee, third on 4428 and Russian Aleksey Drozdov next on 4408.
The two-day, 10-discipline event concludes Friday with the 110m hurdles, discus, pole vault, javelin and 1,500m. Thursday's opening events were the 100m, long jump, shot put, high jump and concluding 400m.
Clay, the 2005 world champion and 2008 world indoor heptathlon champion, achieved the world's highest decathlon score since 2004 at the US Olympic trials with a personal best of 8.832 points, the best US result in 16 years.
The first night ended with Serble crying after his concluding 400m heat, which left him fifth on 4312, needing to make up more than 200 points on Clay in the final five events to keep his crown.
World record-holder Serble, 33, has been nagged by injuries all year, with a left thigh problem at the world indoors in March, another injury to the same leg a month later and a right thigh injury last month.
Krauchanka was this year's world indoor runner-up while Hardee was second to Clay at the US Olympic trials with the season's third-best point total.
Clay led with 2862 points after the morning 100m, long jump and shot put with Sebrle 292 points off the pace in 10th.
After topping the 100 in 10.44 for 989 points, Clay set the pace in the long jump at 7.78m for 1005 points and launched the shot put a person best 16.27m to finish second in the event.
Clay was 11th in the high jump, clearing 1.99.
