They'll compete in the 200-meter freestyle preliminaries on Tuesday morning, with the 16 fastest qualifiers advancing to the evening semifinals. Lochte owns the upper hand in that event, having beaten Phelps at last year's world championships in Shanghai.
Any butterflies two of the world's best swimmers may have felt going into the eight-day meet should be gone since both qualified for the London Games on the first night of the trials. Lochte became the first swimmer to make the U.S. team with his win over Phelps in the grueling 400 individual medley on Monday.
"I can sit down and take a deep breath and relax," Lochte said. "I can just do what I love to do and have fun and just race."
It was a three-man race between world champion Lochte, world record holder Phelps, and Tyler Clary, the fourth-fastest swimmer ever in the event. Each of them owned the lead at different points in the race — Phelps in the butterfly, Clary in the backstroke and Lochte in the breaststroke.
"All three of us were side by side by side and we were neck and neck," Phelps said. "You could hear the excitement of the crowd and that's something that definitely played a pretty big role in giving me a little extra energy the last 150. I was very pleased with that."
Once Lochte took over, he kept on going, building a body-length lead over Phelps and Clary heading into the final 100 meters. He eased up in the closing 20 meters and touched first in 4 minutes, 7.06 seconds. Phelps took second at 4:07.89. Their times were the top two in the world this year.
"That time was not good at all. I know I'm capable of going way faster," Lochte said. "There's definitely a lot of places during that race where I knew I could go faster, I just didn't. I just had to do what I had to do to get my hand on the wall first."
Lochte beat Phelps for the first time ever in the event, snapping a string of nine consecutive losses to his rival in the event dating to 2002.
"It really doesn't say much," Lochte said. "It's a rivalry that we've had for almost eight years now. We've just been switching back and forth. It's hard to say who's the best swimmer because we're both great racers."
Clary came home in third at 4:09.92, a bitter finish for the silver medalist at worlds last year. Phelps didn't swim the event in Shanghai, and since winning it as one of his historic eight gold medals at the 2008 Beijing Olympics he had sworn he wouldn't compete in it again.
Now he's back, and Clary finds himself the odd man out. Clary didn't speak with reporters after the race.
Lochte is entered in 11 events this week, but he was coy about exactly where he'll turn up.
"We're going to pick and choose what events day-by-day and see how I feel," he said.
Phelps didn't win, but he made a little history of his own, becoming the first American male swimmer to qualify for a fourth Olympics.
"We knew that (losing) was a distinct possibility in this event," his coach, Bob Bowman, said. "I don't think we had any illusions. He knows that he's in the range. He knows he can get better."
Peter Vanderkaay made his third Olympic team by winning the 400 freestyle in 3:47.47. He was joined by training partner Conor Dwyer, who finished second.
Elizabeth Beisel became the first woman to qualify for the U.S. team with an easy victory in the 400 IM. She won in 4:31.74 to earn a berth in her second consecutive games. Caitlin Leverenz grabbed the second spot.
Some big names will hit the pool for the first time in Tuesday's preliminary heats. Missy Franklin, the 17-year-old Colorado swimmer tabbed for stardom in London, competes in the 100 backstroke; Amanda Beard opens her quest to make a fifth Olympic team in the 100 breaststroke; and Janet Evans, making a comeback at 40, goes in the 400 freestyle, although her stronger event is the 800 free.
Beard faces a loaded field in the 100 breast that includes world champion Rebecca Soni, former world record holder Jessica Hardy, and 2000 Olympic champion Megan Jendrick, who gave birth to her first child eight months ago.
On Tuesday night, Brendan Hansen goes for a spot on his third Olympic team in the 100 breaststroke. He flirted with the American record in Monday's semifinals, coming up short with a time of 59.71 seconds — fourth-fastest in the world this year. The 30-year-old former world champion quit after Beijing but returned to the pool looking to make up for disappointments in the last two Olympics.
"I went out there and hit the first five strokes and I was like, 'I'm gone, later,' and just took off," Hansen said. "You have no idea how hard it is to break a minute."
Eric Shanteau, who competed in Beijing after being diagnosed with testicular cancer, also advanced.
Dana Vollmer, a 2004 Olympian who failed to qualify for the team four years ago, set an American record in the semifinals of the 100 butterfly. The defending world champion put up the world's fastest time this year of 56.42. Natalie Coughlin, an 11-time Olympic medalist, also made the eight-woman final.