American Natalie Coughlin became the first woman to repeat as Olympic champion in the 100m backstroke on Tuesday, holding off newly minted world record-holder Kirsty Coventry for the gold.

The 25-year-old world champion won in an American record of 58.96 seconds, 19/100ths of a second outside the world record of 58.77 set by Coventry in the semi-finals.

She became the first to break 59sec at the US trials in Omaha, where the record fell three times.

It was broken twice in the space of two minutes in the preliminaries in Omaha when Hayley McGregory grabbed it only to have Coughlin snatch it back in the next heat.

"To win gold in such a strong event, I'm so proud. That's probably why I was crying like a baby up on the stand," Coughlin said.

"I think the 100 back-stroke is progressing faster than any other female event," said Coughlin, who in 2002 became the first woman to swim it in under a minute.

Coughlin said she wasn't surprised to see Coventry break the mark in the Beijing semis, but what really ratcheted up the pressure was knowing no one had won successive titles.

"I heard prior to the meet that it would be the first time, which added a lot of pressure and made me really nervous," she said.

Coughlin was especially pleased that she was able to conquer those nerves.

"For whatever reason, the last few days before the meet I didn't feel as great as I wanted to," she said. "But I got my head together. A lot of it was in my head, but luckily I got it together in time."

It was Coughlin's third career Olympic gold medal and confirmed her as the foremost backstroker in women's swimming.

Coventry took the silver medal in 59.19 with American Margaret Hoelzer third in 59.34.

"It hasn't really sunk in yet," Coughlin said. "When I saw the clock I thought I had made a mistake and I only knew I had won when I saw the number one by my name.

"It's a great feeling, I am overjoyed."

Hoelzer said she was weary after her bronze medal swim but proud of her first medal at the Olympics.

"I'm a little tired to be honest, but I'm very happy, this is my first medal of the Olympics. I'm thrilled," she said.

"It was a close race, the third, fourth and fifth were less than a tenth of a second apart."

Neither Coughlin nor Coventry had time to give in to fatigue, as both raced the semi-finals of the 200m individual medley this morning.

And with her 100m backstroke gold safely around her neck, Coughlin wasn't ruling out the chance that she would yet depart Beijing with the world record.

"There's still the medley relay," said Coughlin, who could reclaim the mark with her lead-off swim in that event for the United States.