World 100-meter champion Carmelita Jeter and sprint stars Sanya Richards-Ross and Allyson Felix made winning starts to London double bids at the US Olympic Track and Field Trials.
And Ashton Eaton, last year's runner-up at the world championships in the decathlon, outclassed reigning world champion Trey Hardee and 2008 Olympic champion Bryan Clay, winning four of the first five events.
The athletes on Friday performed in cold and showery conditions that left puddles on the track in a meet where only the top three in each final advance to next month's London Olympics.
"When you are ready, you are ready, no matter what the conditions," said Richards-Ross after winning her 400-meter qualifying heat in 51.69 seconds. "I'm excited to start the journey to my third Olympic Games."
Richards-Ross, the Jamaican-born 2009 world 400m champion who became a US citizen in 2002, has the best 200 and 400 times in the world this year and ranked third-fastest among 16 qualifiers for Saturday's 400m semi-finals.
In the opening round of the women's 100m, Jeter won her heat in 11.20sec, well off the season's world best of 10.81 she set last month in Jamaica.
"This is going to be a hard team to make," Jeter said. "I have two more rounds. I have got to stay focused."
Felix, a two-time Olympic 200m runner-up who like Jeter is trying to qualify for London in the 100 and 200, won her heat in a wind-aided 11.19 seconds, pushed by a 1.6m/sec tailwind.
"I'm always nervous," Felix said. "It's good to get the first one out of the way. It was OK. I will come back faster tomorrow."
Rain is also in the forecast for Saturday's 100 semi-finals and final.
"You don't think about it," Felix said of the damp conditions. "You just keep pushing."
In the decathlon, Eaton won the 100m in 10.21, the long jump with a leap of 8.21m, the high jump by clearing 2.05m and the 400m in 46.70 to lead after day one with 4,728 points, 322 ahead of Hardee with Clay third on 4,252.
"What you just saw is the culmination of everyone who got me to this point and me trying not to let them down," Eaton said. "I just do not want to let anyone down. Now I've got to get ready for tomorrow."
On Saturday the event concludes with the 110m hurdles, discus, pole vault, javelin and 1,500m.
Hardee, who won the shot put with a heave of 15.72m, said he felt good about his start, noting "I'm in one piece. Just a little tired."
The first two Olympic qualifying finals at Hayward Field were staged in the men's and women's 10,000 meters, with favored Galen Rupp claiming the men's crown in 27min 25.33sec and Amy Hastings taking an emotional women's win in 31:58.36.
Hastings placed fourth in the US Olympic marathon trials earlier this year, the fastest finisher not to earn a spot in London in that race at Houston.
"I cried every day for a month," Hastings said. "It was heartbreaking in Houston. Coming across the finish line today, it felt totally different. I think it sweetens it, though."
Kellie Wells led 21 semi-final qualifiers in the women's 100m hurdles while Lolo Jones was 15th overall in 13.01sec with 2004 Olympic champion Joanna Hayes, making a comeback after having a baby, just behind her in 13.06.
"Nice and easy," Wells said. "Not a whole lot of pressure. Just run and have fun."
Jones was unhappy about a poor start but confident she could recover in Saturday's semi-finals and final.
"I didn't execute my first five (hurdles)," she said. "I realized it was prelims and I relaxed. I lost too much at the start. I am concerned but I know there is a lot of room for improvement.
"Sometimes I run my best races after I do poorly."
Reigning Olympic 400m champion LaShawn Merritt led 16 semi-final qualifiers in 45.36 and was cautious because of the wet conditions, which led to a rival slipping and falling in his heat.
"It was never about winning that race. I wasn't going to push it to win," Merritt said. "It was slippery out there. You don't want to run too hard in this weather. Looking good, though. I am confident."
Jeremy Wariner, the 2004 Olympic champion and runner-up to Merritt in 2008, was 13th-fastest among 16 to advance with a time of 45.84.
"My main goal was to qualify and to get the cobwebs out," Wariner said.