The loss broke a string of 18 consecutive outdoor victories in the 400 for Richards since her runner-up finish at the 2005 world championships.

The two-time defending champion had the five fastest times in the world, capped by an American record, a year ago, but she was dogged by a flulike illness that kept her out of her first four meets this season.

Dee Dee Trotter won her first U.S. outdoor title in a lifetime best 49.64 seconds. South Carolina's Natasha Hastings was second in a college-record 49.84 and Mary Wineberg third at 50.24. Trotter came from third on the final turn to draw away.

Richards, who ran under 50 seconds nine times last year, finished at 50.68.

"I just lost my thinking," Richards said. "I thought I was already on the team and didn't fight for that third spot, so I'm really disappointed. But I still have the 200, and I'm going to come out and win that."

Richards later advanced through the qualifying round of the 200.

"It was really tough," Richards said. "My parents came down and they encouraged me and said that maybe the 400 wasn't for me to win this year. Maybe it's the 200. I tried to get my head back into it. I felt OK in the 200. I didn't feel great. I'm sure it was more mental than physical. Hopefully, I'll run really well tomorrow."

Tyson Gay, running less than 24 hours after his 9.84-second clocking in his 100-meter victory, was the leading 200 qualifier at 20.66 seconds into a brisk headwind. Wallace Spearmon, Xavier Carter and Jeremy Wariner were among the others to advance to Sunday's semifinals.

With Gay, Spearmon and Carter, the event features three of the fastest sprinters in the event's history. A fourth, NCAA 100 and 200 champion Walter Dix, did not show for the 200.

"It's a new day," Gay said. "I really didn't warm up long. I'm a little fatigued. I just wanted to get it done."

The top three finishers in each event make up the U.S. team for the world championships Aug. 25-Sept. 2 in Osaka, Japan. Defending world champions also make the team, as long as they compete in some event at the U.S. meet.