Their first showdown of the London Olympics went to Lochte in a runaway on the opening night of the swimming competition. This one figures to be a lot closer.
The American stars compete against each other for the last time in the 200-meter individual medley on Thursday night. Lochte qualified fastest in 1 minute, 56.13 seconds. Phelps was 98-hundredths of a second back in third.
"We love racing against each other," said Phelps, who plans to retire after the games. "Neither one of us likes to lose. I like to say we bring out the best in one another."
In between them again is Laszlo Cseh of Hungary. He's been the perennial also-ran in the last two Olympics, taking bronze behind Phelps at the 2004 Athens Games and silver four years ago in Beijing when Phelps won and Lochte was third.
Phelps could accomplish one more bit of history on Day 6 at the pool. A victory would make him the first male swimmer to win an individual event in three consecutive Olympics. Japanese star Kosuke Kitajima failed to defend either of his titles in the 100 or 200 breaststrokes, leaving Phelps a chance to accomplish the feat.
He missed on his first two tries at a threepeat, finishing fourth in the 400 IM (Lochte won) and second in the 200 butterfly.
Lochte has a busy schedule on what could be a big night for the U.S. He'll try to defend his title in the 200 backstroke final, with teammate Tyler Clary pressuring him as the fastest qualifier. Then a short time later, Lochte returns for the 200 IM final.
Leading off the night will be Rebecca Soni in the 200 breaststroke final. The American broke the world record in the semifinals with a time of 2:20.00 on Wednesday and will be the heavy favourite to win her second straight Olympic gold medal.
"It's been four years since I swam close to that fast so it's great to be back on top like that," she said. "I'm excited to have one more race. I felt good so all I have to do is feel about the same and hopefully I can go a little faster."
The night wraps up with a new champion being crowned in the women's 100 freestyle final, an all-out sprint to the wall featuring Ranomi Kromowidjojo of the Netherlands and American teenager Missy Franklin.
Kromowidjojo set an Olympic record of 53.05 seconds in the semifinals. Melanie Schlanger of Australia was second-quickest at 53.38 and Franklin was third in 53.59. Defending champion Britta Steffen of Germany failed to make the final.
The U.S. team continued its strong showing with victories by Nathan Adrian in the 100 free and the team of Franklin, Dana Vollmer, Shannon Vreeland and Allison Schmitt in the 4x200 free relay on Wednesday.
Adrian won a thrilling race that came down to the end. He got to the wall one-hundredth of a second ahead of James "The Missile" Magnussen of Australia, becoming the first American to win the 100 free since Matt Biondi at the 1988 Seoul Olympics.
Adrian hit the wall in 47.52 to Magnussen's 47.53. Brent Hayden of Canada took the bronze in 47.80, his country's first-ever medal in the event.
"This guy is an incredible closer. I knew that," Adrian said of Magnussen. "I knew it was going to take a lot more than what I'd ever done before to be able to hang with him those last 5 metres."
Adrian had shown what he could do against Magnussen in the 4x100 free relay, going faster than the Aussie on the opening leg. The Missile came in as the world champion and had swum the fastest time ever in a textile suit (47.10) at the Australian trials in March.
"To have lost that one was shattering," Magnussen said. "To get knocked down again, it's tough."
The Aussies took another bitter defeat to the U.S. in the women's 4x200 free relay. Schmitt chased down Alicia Coutts on the last leg and won going away in 7:42.92. The Aussies settled for silver in 7:44.41, while France took the bronze.
Soni wasn't the only one with a world record Wednesday.
Daniel Gyurta of Hungary lowered the 200 breast mark and won the gold in 2:07.28. Michael Jamieson thrilled the British fans by taking the silver in 2:07.43. Ryo Tateishi of Japan earned bronze.
Jiao Liuyang of China set an Olympic record to win the women's 200 butterfly in 2:04.06. Mireia Belmonte Garcia of Spain finished second and Natsumi Hoshi of Japan was third.