Ryan Lochte downed Michael Phelps in the men's 400m medley at the US Olympic swimming trials in a race that gave a glimpse of the fireworks they could produce at the London Games.
Lochte seized control on the breaststroke leg and held on to beat Phelps for the first time in the punishing four-stroke event.
Lochte won in 4min 7.06sec, while Phelps, the world record-holder and two-time Olympic champion, was second, booking an Olympic berth in 4:07.89.
Tyler Clary, the World Championships silver medallist behind Lochte in Shanghai last year as Phelps opted out of the event, was the odd man out.
He finished third in 4:09.92, but only the top two finishers in each event in the eight-day meeting make the Olympic team.
Lochte, beaten by Phelps in nine prior 400m medley clashes dating back to 2002, said he wasn't trying to make a statement against the 14-time Olympic gold medallist.
"I wanted to win," he said. "I wanted to get on the Olympic team. Now I can just do what I love to do, have fun and race."
After making the 400m medley one of his eight triumphs in Beijing, Phelps had vowed he wouldn't swim it again in major international competition.
"The thing it came down to -- I wanted to do it," Phelps said. "This is an event I've done for a long time and I want to finish off my career doing it."
Phelps became the first male US swimmer to qualify for four Olympics. By qualifying in the 400m medley, Phelps gives himself a chance to become the first male swimmer to win the same event at three straight Games -- although it's clear he'll have his work cut out to beat Lochte.
"That time was not good at all," Lochte said. "I know I'm capable of going faster."
Lochte, Phelps and Clary were already all faster than the previous fastest time in the world this year -- 4:10.26 set by Japan's Kosuke Hagino.
Phelps will also be favoured to punch his ticket in four other individual events, the 100m and 200m butterfly, the 200m free and 200m medley, all of which he won in Beijing.
If he swam all three relays, he could again have an eight-event schedule in London.
Now, however, Phelps will face tough competition from Lochte, who emerged from Phelps's shadow as he won five titles at the World Championships last year.
That included victories in head-to-head showdowns with Phelps in the 200m medley and 200m freestyle.
"Obviously, that's some pretty good competition," Phelps's coach Bob Bowman said. "He just kicked our ass."
Lochte, contemplating a Phelps-style multi-medal attempt in London, entered 11 events at trials. He dropped the 400m freestyle, and said he would tweak his programme as the meet progresses.
"We're going to pick and choose, day by day," Lochte said, noting that his focus was now on Tuesday's 200m freestyle -- another likely showdown with Phelps.
In Monday's other finals, 19-year-old world champion Elizabeth Beisel won the women's 400m individual medley in an impressive 4:31.74, fastest in the world this year. Caitlin Leverenz was second in 4:34.48.
Peter Vanderkaay won the 400m freestyle in 3:47.67 to book a third trip to the Olympics. Conor Dwyer was second in 3:47.83.
Lochte, Beisel, Vanderkaay and Dwyer all train in Florida under coach Gregg Troy, who will also be head coach of the US men's Olympic team.
Dana Vollmer, a 2004 Olympian who didn't make the team for Beijing, set an American record of 56.42sec in the semi-finals of the women's 100m butterfly to lead the way into Tuesday's final.
Former world record-holder Brendan Hansen broke a minute in the 100m breaststroke semi-finals, clocking 59.71sec.