BARCELONA, Spain -- Jenny Thompson's singing voice proved as good as her swimming stroke.

Coming from behind in the anchor leg Sunday, she helped the United States win the women's 400-meter freestyle relay at the world championships.

Thompson now has a record-tying 10 medals from world championships, plus eight Olympic gold medals.

In Sunday's race, she was third with about 25 meters to go.

"There is some power that comes over me when I'm doing relays," Thompson said. "I don't know what it is, but I get very excited. I can't let my team down. There is no option but to win."

But when the four Americans stood on the podium to receive their gold medals, the national anthem didn't play. During the awkward silence, the swimmers fidgeted for several minutes, smiled to friends in the stands and looked slightly embarrassed.

They said they heard only a faint clicking, like a CD skipping.

But no anthem.

So as the red-white-and-blue flag was finally raised, the four teammates _ Thompson, Natalie Coughlin, Lindsay Benko and Rhiannon Jeffery _ sang a cappella.

Organizers apologized and even offered to redo the ceremony Monday. The same thing happened two years ago at the worlds in Fukuoka, Japan, when the Spanish anthem didn't play after a gold in water polo.

"I've always wanted to be a rock star, so starting out with the anthem is a good way," Thompson said. "I have to believe it was an honest mistake and they formally apologized to us. It's not a big deal. We have no hard feeling."

Coughlin said teammates in the stands got them going.

"We were wondering what was going on," Coughlin said.

Who has the best voice?

"I already told them I did," Coughlin said.

Thompson didn't buy that.

"It's a controversy," she said. "We'll have to make a demo."

The Americans' winning time was 3 minutes, 38.09 seconds. Germany won the silver (3:38.73), followed by Australia (3:38.83).

Thompson also swam the top time in the 100 butterfly semifinals (57.99). The final is Monday.

Thompson has completed two years at Columbia medical school and has cut her training. Eighteen months ago she was barely swimming at all, working out in a tiny 15-yard pool at the university.

Less seems to be better for a woman many consider the greatest relay swimmer in history.

Coughlin, meanwhile. is billed as the best American woman in a generation and is expected to swim seven events by the time the worlds end next Sunday. She already holds the world record in the 100 backstroke (59.58).

Three other medal events in the pool highlighted the first of eight days of swimming.

Ian Thorpe remained unbeatable in the 400 freestyle, finishing in 3:42.58 to stay unbeaten in the event for six years. Another Australian, Grant Hackett, was second, with Romania's Dragos Coman third.

Thorpe was ill four months ago with a virus and has changed coaches, leading some to suggest he's not as dominant as a year ago, when he set his 400 world record of 3:40.08.

"I don't feel like I've reached my absolute peak in that event or any event," Thorpe said.

He's the first swimmer to win three straight world titles in an event. His ninth gold medal also made him the first man to win that many at world championships in a career.

Hannah Stockbauer of Germany won the women's 400 freestyle in 4:06.75. Diana Munz of the United States was third.

The Russians, anchored by four-time Olympic champion Alexander Popov, won the men's 400 freestyle relay in 3:14.06, 0.74 ahead of the second-place United States.

The diving wrapped up Sunday with Australia winning the men's 10-meter synchronized platform, and China taking the 3-meter women's springboard synchronized title.

China led all countries with 12 diving medals, including four golds.