BEIJING -- Aaron Peirsol won the men's Olympic 100-meter backstroke on Tuesday, defending his title with a world-record time and extending the United States' dominance of the event.
Peirsol touched in 52.54 seconds, lowering his old mark of 52.89 set at last month's U.S. trials.
"It never gets old," said Peirsol, who swept the backstroke golds in Athens and will try to do the same in Beijing. "It really does feel like the first time."
Teammate Matt Grevers earned the silver in 53.11, added to the gold he won for swimming the preliminaries of the 400 free relay. Arkady Vyatchanin of Russia and Hayden Stoeckel of Australia tied for the bronze in 53.18.
The U.S. has won the men's 100 back at four consecutive Olympics, with Peirsol taking the title in Athens in a time that was 0.17 seconds slower.
In the women's 100 back, Natalie Coughlin of the United States became the first woman to ever defend her title in the event, winning with an American record of 58.96.
"It hasn't really sunk in yet," said Coughlin, who claimed her seventh Olympic medal overall. "I knew when I saw the '1' by my name, because at first I thought I saw the clock wrong. It's a great feeling.
World record-holder Kirsty Coventry of Zimbabwe earned the silver in 59.19. Another American, Margaret Hoelzer, took bronze in 59.34. Six of the eight finalists swam under 1 minute.
Coughlin earned her second medal of the Beijing Games, having won a silver in the 400 freestyle relay. Coventry was the silver medalist in the 400 individual medley.
"I'm so glad to have this race behind me because there's so much pressure," Coughlin said. "I tried to keep myself as mentally strong as possible."
The U.S. dominance was broken only by Australia's Leisel Jones, who made up for a disappointing bronze four years ago by winning the 100 breaststroke in 1:05.17, just eight-hundredths off her own world record. Rebecca Soni, who only got in the event after fellow American Jessica Hardy tested positive for drugs last month, took advantage of her opportunity by winning the silver in 1:06.73.
"It almost felt like less pressure because it wasn't initially my event," Soni said. "I don't think it's necessarily fair what happened, but rules are rules and I'm just doing what I'm told."
Mirna Jukic of Austria got the bronze (1:07.34).
In the semifinals of the women's 200 free, Katie Hoff advanced with the second-fastest time of 1:57.01. The 19-year-old American, who's like a little sister to Michael Phelps, is still trying to win her first gold medal after settling for bronze and silver in her first two events. She still has three more individual races, plus a relay, to make up for that void.
Slovenia's Sara Isakovic was the top qualifier at 1:56.50.
Hoff returned to post the third-fastest time in the semifinals of the 200 individual medley, trailing Coventry (2:09.53) and Australia's Stephanie Rice (2:10.58) in 2:10.90. It also was a busy morning for Coughlin, who won the other heat in the 200 IM with the fourth-best time overall, 2:11.84.
Later, cancer-stricken Eric Shanteau made his Olympic debut, easily advancing out of the 200-meter breaststroke preliminaries just a couple of weeks before he will undergo surgery.
Carrying the hopes of cancer survivors he's heard from since going public with his diagnosis last month, Shanteau smoothly stroked his way through the four-lap race and qualified seventh in 2 minutes, 10.29 seconds.
"This was the longest day of my life," he said. "That's why I'm glad finals are in the morning because you wake up, you race and you're not sitting around thinking about it all day."
Defying conventional medical wisdom, Shanteau decided to put off surgery to compete in the Olympics, but only after being checked repeatedly to make sure the cancer wasn't spreading and threatening his chances of a full recovery.
He found out he had testicular cancer just weeks before last month's U.S. trials, where he upset Brendan Hansen to earn a trip to China.
"It was weird walking on deck," Shanteau said. "I was totally clear -- not too many nerves, excited, but pretty calm. It almost didn't feel like the Olympic Games. That was probably good in a sense."
He moves on to the semifinals on Wednesday morning. The finals are Thursday morning.
While Phelps slept in the athletes' village, his teammates set him up to claim another gold medal by qualifying fastest in the 800 free relay.
David Walters, Ricky Berens, Erik Vendt and Klete Keller combined for a time of 7:4.66 seconds, lowering the Olympic record of 7:07.05 set by Australia at the 2000 Sydney Games.
Their effort guaranteed Lane 4 for Phelps and the rest of the relay team, which goes for its second consecutive Olympic title in a U.S.-dominated event.
The Americans finished a whopping 3.18 seconds ahead of second-place Italy, making another gold for Phelps seemingly inevitable. He is 3-for-3 in his events so far.
Vendt was inspired for his swim by watching Shanteau.
"He's just a great guy," he said. "The fact he even went through that at trials and still came out on top way he did says so much about who he is and what he is."
American Jason Lezak, fresh off his stunning anchor leg in the victorious 400 freestyle relay, also qualified in the 100 free preliminaries.
Lezak has some work to do, though, if the 32-year-old Californian is going to make the 100 free final. He moved into the semifinals as 11th-fastest, with a time of 48.33 seconds.
That was considerably slower than the amazing 46.06 anchor leg he swam to lead the U.S. to a world record and gold medal in Monday's relay. He outtouched former world record-holder Alain Bernard of France at the wall, barely preserving Phelps' run at Mark Spitz's record of seven gold medals in a single Olympics.
"It was definitely difficult because last night was a finals situation," Lezak said. "I really didn't have the focus I did yesterday. I was just looking to get out of my heat. I've got more races ahead of me that are more important."
Eamon Sullivan of Australia, who broke the world record on the relay's leadoff leg Monday, was fastest of all, at 47.80.
"I think emotionally it probably did take a little bit out of me, but I've been very careful about what I've been doing and reacting to that," Lezak said. "Just play it down and enjoy the moment and focus on the days ahead. That's why I was trying to hold back a little bit, so I didn't blow my tank and I can swim fast tomorrow morning."
Stefan Nystrand of Sweden was second-quickest in 47.83, followed by Canadian Brent Hayden (47.84) and Bernard (47.85). Two-time defending champion Pieter van den Hoogenband of the Netherlands moved on in fifth with a time of 47.97.
Like Lezak, Garrett Weber-Gale was trying to come down from the emotional high of the relay that had the Water Cube buzzing a day later. Weber-Gale held the eighth spot at 48.19 in an event that no American has won since Matt Biondi in 1988.
"I was so excited the whole day. It was just truly spectacular," he said. "Now we need to move on and swim fast. There's a lot of fast swimmers. I know I'm capable of doing a lot, and that's what I plan on doing."
Fabien Gilot, who joined Bernard on the French relay, also advanced. South African sprint star Ryk Neethling failed to advance in 32nd.
Information from The Associated Press was used in this report.