OMAHA, Neb.—Katie Hoff made it 2-for-2 at the U.S. Olympic trials.

And she’s just getting started.

Showing no signs of tiring, the Baltimore teenager gutted out another grueling win Monday night, rallying to win the 400-meter freestyle just 24 hours after she set a world record in the 400 individual medley.

Hoff became the first U.S. swimmer to lock up two races in Beijing, but there’s no time to savor her accomplishment. She’s already done about a mile of races in Omaha and plans to compete in four more before the week is out, pursuing an Olympic program just slightly less ambitious than the one Michael Phelps will attempt in hopes of knocking off Mark Spitz.

As for Phelps, the birthday boy had a relatively light day as he turned 23, easily qualifying for Tuesday’s final in the 200 freestyle to set up another showdown with Ryan Lochte. On the meet’s opening night, both eclipsed the old world record in the 400 IM, but Phelps touched the wall first.

Two more world records fell on day two—both in the morning preliminaries, about 2 minutes apart. Hayley McGregory knocked off Natalie Coughlin’s 4 1/2-month-old mark in the 100 backstroke with a time of 59.15 seconds, only to have Coughlin take it right back in the next heat at 59.03.

They pulled back in the evening semifinals, clearly wanting to save something for their head-to-head matchup Tuesday.

Brendan Hansen had a big letdown in the 100 breaststroke, despite locking up a second straight trip to the Olympics.

After just missing the world record in the semifinals, Hansen got off to a sluggish start and struggled home with a time of 59.93, good enough to win but nearly a full second off the record of 59.13. He glared at the scoreboard, stared at the water, then shook his head slightly.

“I’m a little disappointed, obviously, at the time, but you can’t be mad about the fact of making your second Olympic team,” Hansen said. “If I had to pick a place to break that world record, it would be at the Olympics. I’ve done it at the trials before (in 2004) and it’s fun, but it’s a lot more fun when you break it at the Olympics.”

Christine Magnuson won Monday’s other final, claiming her first trip to the Olympics with a win in the 100 butterfly.