Ryan Lochte swims his men's 200m individual medley heat during the U.S. Olympic swimming trials.

Omaha, Nebraska - Michael Phelps and Ryan Lochte set themselves up for another mouthwatering showdown at the U.S. Olympic swimming trials when they qualified for the semifinals of the 200 metres individual medley on Friday.

The pair, who have already gone head-to-head in the 400 medley and 200 freestyle, won their heats to safely advance to the next round.

Phelps, who won the 200 medley gold medal at the last two Olympics, clocked one minute 59.27 seconds, the second fastest time overall behind Conor Dwyer (1:59.11).

Lochte, the world champion and world record holder, stopped the clock at 1:59.92, the fourth best time, but was conserving his energy after swimming two events in the session.

The 27-year-old also set the quickest time in the 200 backstroke preliminaries less than two hours earlier and said he was carefully managing his programme.

“The 200 backstroke is probably one of the hardest events known to swimmers,” Lochte said. “It just takes away your legs especially when you have to get on the blocks and race Michael Phelps.”

Dana Vollmer, winner of the 100 butterfly, topped the qualifiers in the women's 100 freestyle in 54.35, just ahead of

Allison Schmitt (54.49) who won the 200-400 freestyle double.

Jessica Hardy, the 100 breaststroke world record holder, was third while teenage prodigy Missy Franklin was seventh and Natalie Coughlin ninth.

The top eight swimmers from Friday night's semis qualify for Saturday's final, with the top two booking their places for next month's London Olympics.

Olympics champion Rebecca Soni set the fastest time in the preliminaries of the women's 200 breaststroke, stopping the clock at 2:23.11.

Amanda Beard, the gold medallist in Athens in 2004, was fifth quickest as she strived to qualify for her fifth Olympics. – Reuters