Michael Phelps raced early in the morning and well into the evening and twice in between. He raced at 10 a.m., 11 a.m., 6 p.m. and 7:15 p.m. Wednesday, a whole lot of work to earn nothing more than the opportunity to work again.

Phelps's most physically demanding day of the eight-day 2005 world swimming championships at Jean-Drapeau Park offered him not a single chance for a medal. He didn't get to hear the national anthem once, even though he did his job impeccably.

By advancing through two heats each of the 100-meter freestyle and 200 individual medley, Phelps got quite a workout while putting himself in position for a pair of medals Thursday night.

"I wouldn't say it's a piece of cake," Phelps, 20, said. "I'm used to doing multiple races every day. That's what I did growing up . . . [but] I don't want to say it's second nature. At this level it's a little tougher than at the local Baltimore level."

Phelps, who was born in Baltimore but now trains in Ann Arbor, Mich., also continued to distance himself -- in his mind and on the calendar -- from his devastating opening to this meet on Sunday, when he failed to advance to the final of his first event (the 400 freestyle).

Phelps swam his seventh, eighth, ninth and 10 races of the meet Wednesday, leaving himself with a possible seven remaining. Besides the 100 free and 200 medley finals, he also has the heats, semifinals and final, of the 100 butterfly along with as many as two more relays. He has won gold medals in the 200 free and 4x100 freestyle relay.

"I'm feeling good," Phelps said. "After [Thursday], it's sort of downhill from there."

Phelps, who at the 2003 world championships in Barcelona set five individual world records -- including some during semifinals -- swam easy laps in the practice pool and munched on energy bars between the morning and evening races.

He has not managed such electrifying success here, but this seemed destined to be a rockier meet even before it got underway. Phelps decided not to compete in the 200 fly and 400 medley, two events in which he holds world records, substituting two events in which he is less experienced: the 100 and 400 free. Even so, he shocked his rivals Sunday when he finished 17th in the morning heats of the 400 free, failing to advance to that night's final.

"He's one of my best friends," said University of Michigan swimmer Davis Tarwater. "You walk a fine line. I don't think he wanted to talk much about that. . . . I don't think anyone had any doubt he would bounce back. He got his game face on. I think it woke him up."

Phelps finished with the fifth-best time in the 100 free semifinals (48.93). He trailed only fellow American Ryan Lochte in the 200 medley (1:58.36).

Larsen Jensen swam the race of his life in the 800 final, setting an American record and beating his personal best by more than two seconds with his finish in 7:45.63. Yet he spent the race feeling uncertain about the quality of his effort. That's because he trailed Aussie Grant Hackett by more than five seconds at the 300-meter mark and could barely stay within sight of him as the race wound down.

"I sort of figured he was going for the world record," Jensen said. "At least I hoped so, being that far behind him."

Hackett, the 1,500 world record holder, surpassed by 1.49 seconds the world record set four years ago by countryman Ian Thorpe -- a race in which Hackett also broke the world record but had to settle for second place. Hackett, who was congratulated after the race by Phelps, hit the wall in 7:38.65.

Germany's Mark Warnecke, who competed in his first Olympics in 1988 and set the world record in the 50 breast 10 years ago, won the 50 breast final and became the oldest swimming world champion in history, at 35. Warnecke, a physician who said he trains just two hours a day, touched the wall in 27.63 seconds, topping American Mark Gangloff, who claimed his first major international medal (27.71).

"I like swimming, I like the sport," Warnecke said. "For me, it's just enough to swim here [at the world championships]. If you can swim here and not the masters' championships, why not here?"

Warnecke said he adds targeted weight training to the approximately 4,000 meters he swims daily.

"If you do it all together, you can swim fast in the 50," he said. "The 100 is more complex. . . . There you feel the age."

Gangloff, 23, of Akron, Ohio, said he didn't know what to expect from this event, which is not contested at the Olympics and is rarely swam in the United States.

"I've never swum the 50 breast in my life," he said. "It was kind of a new event for me mentally."

Italy's Filippo Magnini, front, and American Michael Phelps look at the results after competing in a semifinal heat of the men's 100-meter freestyle.