Phelps came from behind in his 200 fly preliminary heat, winning in 1 minute, 57.36 seconds. He tied Takashi Yamamoto of Japan for first among 16 qualifiers heading into the evening semifinal.
Phelps' quest to break Mark Spitz's record of seven gold medals at the 1972 Munich Games was dashed with the Americans' bronze medal in the relay Sunday night. The South Africans won gold in a world-record time and the Netherlands took silver.
"We really wanted that relay," Phelps said.
Phelps can still tie Spitz's elusive mark if he wins his four remaining individual races and swims on the other two relays. The 19-year-old from Baltimore has one gold so far, in the 400 individual medley.
"It was a little hard after last night," he said. "It took a lot out of me emotionally, for sure. I wanted a strong one this morning."
Yamamoto swam next to Phelps, but he wasn't paying attention.
"I'm just hoping to qualify for the final," he said.
Phelps is the world record holder in the event. Four years ago, he finished fifth in the 200 fly — his only event at the Sydney Games.
Tom Malchow, the defending Olympic champion, was fourth-fastest in 1:57.75 despite swimming with an injured right shoulder. He was nine-hundredths of a second behind Pawel Korzeniowski of Poland, who was third in 1:57.45.
Phelps had a busy Monday night ahead of him. He was to swim the much-hyped 200 free final — a showdown with Australian Ian Thorpe and defending Olympic champion Pieter van den Hoogenband — followed by the 200 fly semifinal.
"He just wanted to be in that race. I have no idea if he can win or not, but I think he'll put up a really good time," his coach Bob Bowman said.
"If the seven gold medals was any consideration, there's no way he would have done the 200 free. He would have put all his eggs in the relay basket and rested up tonight, but he wants to see what he can do."
Bowman indicated that Phelps was not obsessed with equaling Spitz's record.
"It's not the center of his being," the coach said. "It's a good publicity thing if he can keep winning, but I don't think he's sitting over there saying, 'I've got to win the 200 free.'"
American Dana Vollmer had the fastest preliminary time in the women's 200-meter freestyle preliminaries while swimming in the same heat as 2000 silver medalist Martina Moravcova of Slovakia.
"I kept it smooth," said Vollmer, who clocked of 1 minute, 59.49 seconds. "I definitely feel like I can go a lot faster tonight."
Claudia Poll Ahrens of Costa Rica, the 2000 bronze medalist and 1996 Olympic champion, was second-fastest in 1:59.50 and also advanced to the semifinals. Her heat included world record holder Franziska van Almsick of Germany, who was ninth in 2:00.21.
Van Almsick is a two-time silver medalist competing in her third Olympics.
Moravcova barely advanced, claiming the 15th spot among the 16 qualifiers for the evening semifinal.
Vollmer has a rare condition that could cause her heart to beat rapidly — then suddenly stop. If that happens, death can occur within minutes.
She had another heart-related ailment that was corrected through minor surgery. But doctors also diagnosed "long Q-T" — a hereditary disorder of the heart's electrical rhythm that can occur in otherwise healthy people.
Vollmer's mother brings along a defibrillator to all her daughter's meets, ready to spring into action if the unthinkable happens.
"Normally, I don't get too nervous, but I was pretty nervous," the teenager said. "I just told myself to calm down and it would be OK."
In the 200 individual medley, Kristy Coventry of Zimbabwe led the way in 2:13.33. Defending Olympic champion Yana Klochkova of Ukraine, who won the 400 IM Saturday, was second in 2:13.40.
15-year-old American Katie Hoff was third in 2:14.03.
In other Olympic news:
International judo officials canceled a meeting Monday to investigate whether a two-time champion from Iran who reportedly said he wouldn't fight an Israeli opponent deliberately avoided the first-round bout by showing up overweight.
International Judo Federation spokesman Michel Brousse said that some officials were unable to attend the meeting on Arash Miresmaeli and could not say when the IJF would next meet.
Miresmaeili, a favorite in the under-66kg class, was declared overweight at the morning weigh-in and disqualified for his first-round bout against Ehud Vaks.
Iran does not recognize Israel and bans any contact with the Jewish state.
Iranian athletes have refused to compete against Israelis in the past. At the 2001 judo world championships, Mahed Malekmohammadi of Iran did not compete again Yoel Razvozov.