Michael Phelps outdueled Ryan Lochte to win the 200 metres individual medley at the U.S. Olympic trials on Friday while Katie Ledecky suffered her first setback on the road to the Rio Games.

While Phelps and Lochte's breathtaking showdown added another thrilling chapter to their great rivalry, Tyler Clary closed the book on his career after a third place in 200 backstroke ended his hopes of defending the gold medal he won at the 2012 London Games.

"I don't see any reason to continue," said Clary.

"I'm looking forward to turning the page and starting a new chapter."

Ledecky, 19, had dominated the women's freestyle events but finished seventh in the 100, which was won by Abbey Weitzeil in 53.28 seconds.

Having already collected wins in the 200 and 400, Ledecky's transformation from distance diva to speed queen hit a bump, denting her hopes of landing a spot on one of the US relay teams.

The top six finishers are all placed in the US relay pool.

"Got seventh, that's what happened," shrugged Ledecky.

"Kelsi (Worrell) was eighth and we're both already on the team so if they want us in the relay, they can put us in if somebody get sick, we'll be there."

Ledecky was much more impressive in her 800 morning heats, where the world record holder and Olympic champion was the top qualifier after clocking the third best time ever in the event of 8:10.91.

Phelps and Lochte provided the highlight of the night, and perhaps the entire week, with their battle in the 200 IM.

The race marked the last time Phelps and Lochte will go head-to-head in an American pool but the two swimming giants, who between them have amassed 33 Olympic medals, could clash one final time at the Rio Olympics.

Phelps, who had already qualified for a fifth US Olympic team, held off his hard-charging rival to narrowly get to the wall first in one minute, 55.91 seconds, the second-fastest swim in the event this year.

"Ryan and I always have great races with one another," said Phelps.

"Him and I have been racing since 2004 and think when we race each other we bring each other to a different level. We take each other to that next step."

While Lochte was done for the night, Phelps still had work to do, capping off a long, gruelling and emotional day by finding enough in the tank to qualify sixth fastest for the final of the 100 butterfly.

Competing in her first Olympic trials, 19-year-old Lilly King completed the breaststroke double, touching first in the 200 in 2:24.08 and adding the title to the 100 she won on Tuesday.

Ryan Murphy, another first time Olympian, will also be pulling double duty in Rio, getting to the wall first in the 200 backstroke in 1:53.95 ahead of Jacob Pebley and Clary. He also won the 100 backstroke.