Lochte, Phelps vie for individual gold at Pan Pacs
Michael Phelps at the start of the 100m final at the Pan Pacific Championships in Gold Coast on August 22, 2014 - by Patrick Hamilton
Lochte was two-hundredths of a second quicker than Phelps from their respective heats as they vie for their first individual gold medal at the Gold Coast meet.
Lochte clocked 51.55 seconds while 18-time Olympic gold medallist Phelps finished strongly to win his heat in 51.57.
Swimmers had to contend with blustery wet conditions in the coastal outdoor pool on the third day of the four-day meet, featuring swimmers from United States, Australia, Japan, Canada and 14 other nations.
"It's crazy with the sideways rain. It's a little chilly out there, but we're all under the same conditions," Phelps said after his swim.
"So I think people can put it behind them. I think we've done a pretty decent job not worrying too much about this and trying to go out and swim."
The greatest Olympian is looking to win his first individual title after claiming a gold medal as part of the United States' 4x200m freestyle relay on Friday, adding to his haul of international titles just four months into his comeback.
"I'm still learning so much about myself and so much about what I need to do," Phelps said of his return to swimming.
"I am learning and I'm trying to overcome some of the stuff that we have down here (Australia) and I think it'll make us all stronger."
American wonder teen Katie Ledecky is on track for her fourth gold medal at the Pan Pacs after topping the preliminary times in the 400m freestyle.
Ledecky coasted home in a meet record 4:03.09 in the rain, not far outside the 3:58.86 world record she set in the event at the US Championships earlier this month.
"I just wanted to make the finals for tonight," Ledecky said.
"I didn't have any goals time-wise. I feel fine, once you get in the water you don't feel it too much.
"I get my strokes above the water and kind of stay above the wind on it too, so it's not affecting me too much."
The 17-year-old schoolgirl has already won the 200m and 800m freestyle events as well as being part of the winning American 4x200m freestyle relay team.
South Korea's Olympic silver medallist Park Tae-Hwan was the fastest qualifier in the men's 400m freestyle, clocking 3:46.10.
Park was 0.10sec ahead of American Connor Jaeger, winner of the 1500m freestyle earlier in the meet, and Australia's David McKeon.
Australians Alicia Coutts and Emma McKeon were the fastest in the women's 100m butterfly heats, while Commonwealth Games champion Belinda Hocking edged American Missy Franklin by one-hundredth of a second as top qualifier in the women's 200m backstroke.
Japan's Ryosuke Irie is on track to complete the men's backstroke double at the meet with the fastest time of 1:55.10 in the 200m event.