Having been handed "a pretty good beatdown" by the German in the 200-meter freestyle two years ago in Rome, Phelps gets a long-awaited chance at revenge in the world championships.
Biedermann trounced Phelps and took away his world record in Rome, where everyone was wearing the high-tech bodysuits that are now banned.
This time, it should be a fair fight.
Phelps and Biedermann won't be going one-on-one, though. They'll be joined by what Phelps described as "a studly field" in Tuesday night's final at the Oriental Sports Center.
"It's going to be down to the last 50 (meters)," Phelps said. "There are some guys that have front-half speed and some guys that close extremely well. You can probably guarantee that it's going to be a tight group."
Lochte didn't swim the 200 free in Rome, but he figures to be a major presence this time.
"It's going to be definitely a dogfight," he said, noting that he and Phelps will swim next to each other.
"I'm going to kind of move over to the lane line and draft off him. Hopefully we can put something together and pull out a 1-2 race."
Biedermann predicted the final will be "big pressure."
The Americans earned their first gold medal on Monday, with Dana Vollmer winning the 100 butterfly in 56.87 seconds.
No world records have been set in the first two days of the meet, with everyone wearing textile suits.
He let out a yell after touching in 23.10, then took off his goggles and cap and began sobbing while hanging on the lane rope for several seconds.
"Very happy, very relieved," Cielo said.
He cried again during the awards ceremony, and the Chinese fans responded with loud applause.
"I'm an emotional man. My life and career are of great passions," Cielo said. "The gold means a lot to me, and it's very hard to get it."
Dale Oen led from start to finish to take gold in the 100 breaststroke, then pointed to the Norwegian flag on his cap in honor of the people killed during the twin attacks in his country.
"In a time like this for Norway, we need to be together, to be one," he said. "I hope my results here can bring back some confidences and I will go back to help them after the championships."
In the 50 fly, Aussie Matthew Targett took the silver in 23.28 and his 32-year-old teammate Geoff Huegill earned the bronze in 23.35.
Cielo and three teammates tested positive for furosemide, a banned diuretic, at a meet in Rio de Janeiro in May. After the Brazilian swimming federation gave Cielo a warning, swimming governing body FINA appealed the decision to the CAS, which upheld the Brazilian ruling.
Cielo said he consumed the drug in a contaminated batch of a food supplement he regularly uses.
"I'm so glad that I can be here to swim," he said. "The gold medal encourages me to train harder and go higher in the future."
The ruling prompted an outcry from other swimmers, who called it unfair, and there were some whistles in the crowd after his victory.
"It's difficult for him," Targett said. "I'm not going to speak for my friend, but I lived with the guy and I know exactly what he's going through. At times like this, you find out who your real friends are."
Dale Oen was timed in 58.71 for his victory. Fabio Scozzoli of Italy took the silver and Cameron van der Burgh of South Africa won the bronze. Olympic champion Kosuke Kitajima of Japan finished fourth.
Host China claimed its first gold when 15-year-old Ye Shiwen rallied from fifth to first during the freestyle leg in the women's 200 individual medley. She won in 2:08.90.
Olympic champion Stephanie Rice of Australia was fourth, followed by American Caitlin Leverenz.
It was Coutts' second silver medal of the night. She lost to Vollmer in the 100 fly, with Lu Ying of China finishing third.
American Amanda Beard finished 15th and didn't advance.
In Tuesday's final, Soni has a strong chance to become the first swimmer to break a long-course world record since the return to textile suits 1½ years ago.
"I don't worry about that, it just puts too much pressure," she said. "If I do, that's great. If not, it's OK. I'm just going to have fun with it."
Olympic champion Natalie Coughlin of the United States advanced to Tuesday's 100 backstroke final with the fastest time of 59.38.