COLUMBIA, Mo. — Kirsty Coventry of Zimbabwe broke a 16-year-old world record in the 200-meter backstroke today.

The reigning Olympic champion in the event, Coventry toppled the second-oldest world record on the books at the Missouri Grand Prix.

Coventry finished in 2 minutes, 6.39 seconds, which was 0.23 seconds faster than the mark set by Krisztina Egerszegi of Hungary in August 1991. Second-place finisher Margaret Hoelzer was more than 4 seconds behind.

Another longtime record fell when Katie Hoff set the American mark in the 400-meter freestyle. And the meet's marquee attraction, six-time Olympic gold medalist Michael Phelps, didn't disappoint in easily winning the 200-meter butterfly.

The Missouri Grand Prix is holding finals in the morning to prepare swimmers for the same setup at the Beijing Olympics.

"This is the first time I've swam (finals) in the morning," said Coventry, who attended Auburn and trains in Austin, Texas. "Usually, I swim a lot faster at night."

Hoff broke the oldest American record on the books. The 400 freestyle mark was set by distance great Janet Evans in 1988, more than eight months before Hoff was born. Her time of 4 minutes, 2.2 seconds beat second-place finisher Kate Ziegler by more than 6 seconds and was just 0.07 seconds off the world mark.

Hoff also won the 100 freestyle.

"It's just an honor to break one of her records," Hoff said of Evans. "She was considered the distance queen."

Phelps won his only race of the day in 1 minute, 53.31 seconds, more than 3 seconds ahead of runner-up Kaio Almeida.

Phelps, who is still recovering from breaking a bone in his right wrist four months ago, was pleased with his performance, his second-best in the event. He set a world record in the 200 butterfly at last year's inaugural Missouri Grand Prix.

"With everything that happened this year, it's a step in the right direction," he said. "It's a confidence booster."