OMAHA, Neb. — Holding off one of his best friends, Michael Phelps started his second attempt to break Mark Spitz's Olympic record with another epic swim.

Less than an hour later, the teenager he compares to a little sister joined Phelps in the record book.

Phelps set a world record in his first event of the U.S. Olympic swimming trials, touching just ahead of Ryan Lochte to win the 400-meter individual medley in 4 minutes, 5.25 seconds yesterday.

Katie Hoff matched her former North Baltimore teammate in the 400 IM, taking down the women's mark in 4:31.12.

Wearing the high-tech Speedo LZR Racer, Phelps beat his own mark of 4:06.22, set at last year's world championships in Australia when he turned in one of the greatest performances in swimming history with seven gold medals.

After saying he had no fear of Phelps, Lochte proved it by also going under the previous record. But his time of 4:06.08 was only good enough for second with Phelps in the next lane over.

"That was probably one of the most painful races of my life," the winner said. "Everything was left in the pool. I definitely would not have been able to do it without Lochte beside me. He's a great friend and a great competitor. I love racing him."

The 19-year-old Hoff — playfully described by Phelps as the little sister he never had — showed no signs of the nervousness that ruined her first trip to the Olympics four years ago. The youngest member of the U.S. team, she was overcome by the moment and threw up on deck after failing to advance from her first event.

All grown up, Hoff dipped under record pace on the breaststroke leg and held on with her freestyle to beat Stephanie Rice's mark of 4:31.46, set in March at the Australian Olympic trials.

"Stephanie really raised the bar when she broke my old record," Hoff said. "I'm just excited for Beijing, and I think it's going to be a really tough challenging race with her."

Like Phelps, Hoff also was wearing the revolutionary Speedo suit, which has been worn for 40 of the 44 world marks set since it was unveiled in mid-February.

"It definitely gave me a few tenths," Phelps said. "At the end, when I was getting a little tired, the suit gave me a little extra edge."

Larsen Jensen, also wearing the LZR, set an American mark in the 400 freestyle in a three-way race to the wall with previous recordholder Peter Vanderkaay and Erik Vendt.

Jensen's time of 3:43.53 topped Vanderkaay's mark of 3:43.82, which was set last month in California. Vanderkaay also went lower, touching second in 3:43.73.

Brendan Hansen just missed another world record in the 100 breaststroke semifinals, advancing to today's final in 59.24. He holds the mark of 59.13, and nodded his head confidently when he looked toward the scoreboard.

Christine Magnuson was the top qualifier in the semis of the 100 fly in 57.50 — less than a second off Inge de Bruijn's 8-year-old world record.

Phelps was slightly off world-record pace after the opening butterfly, but he had a body-length lead on Lochte as they switched to the backstroke.

The minus sign — indicative of a swimmer under record pace — flashed on the board when Phelps made his flip turn on the back, sending the crowd at the Qwest Center into a frenzy. But Lochte was starting to close the gap, and he nearly pulled even as they headed toward the far wall in the breaststroke.

Lochte, a world recordholder himself, was less than a second behind at the 300 mark and looked poised to pull off an upset. He and Phelps went at it stroke for stroke over the final two laps, but Phelps never relinquished his lead.