Former Olympic 100 metres champion Maurice Greene suffered a shock defeat in the Adidas Track Classic at the Home Depot Center in California on Sunday in a race marred by equipment problems and two false starts.
Greene finished fourth in a race won by fellow American Leonard Scott, who recorded an impressive 10.03 seconds running into a stiff headwind.
"I guess I've got too much power," said Greene, before adding his blocks had slipped in both the second false start and the actual race.
However, the 30-year-old American said the defeat did not represent a setback in his preparations for next month's US national championships at the same venue.
"I'm prepared for the nationals. I'm going to bring my own blocks and they are going to stick," he told reporters.
Olympic champion Jeremy Wariner won the men's 400 metres in 44.53 seconds with key rival and Olympic silver medallist Otis Harris trailing in last after appearing to be unsettled by a false start.
"I felt great the whole race," said the 22-year-old Wariner, adding the hot sunshine did not bother him as he was used to similar conditions when training in Texas.
Olympic gold medallist Veronica Campbell powered to victory in the women's 100 metres in 10.96 seconds, the fastest time in the world this year. The 23-year-old Jamaican won gold in the 200 metres in Athens plus bronze in the 100 metres.
"It was a very good race," said Campbell. "This is a good thing, running 10.96 seconds at the end of May. I think my season is going well."
The Jamaican added that last year she did not set her personal best of 10.91 seconds until the end of the season.
Olympic champion Joanna Hayes won the women's 100 metres hurdles in a time of 12.64 seconds, a world best mark for 2005.
"Overall I'm pretty pleased with it," said the 28-year-old American. "Hopefully next time I will drop it under 60 [12.60 seconds]."
Olympic silver medallist Bernard Lagat produced the fastest time by an American this year in winning the men's 1500 metres.
The 30-year-old Lagat, who won his Olympic medal for Kenya, became a US citizen just under two months ago.
"It shouldn't take long to break the American record," said Lagat, who added that citizenship switch had not been well received in Kenya.
"It's a touchy subject there. But my reasons for wanting to become an American citizen are legitimate. It's not about money, but a question of my future, what I'll do after my career."