COLUMBIA, Mo. — Five-time Olympic medal winner Natalie Coughlin set a world record in the 100-meter backstroke tonight during a preliminary race at the Missouri Grand Prix.

Coughlin finished the race in 59.21 seconds, lowering her previous world record in the event by 0.23 seconds. The world record was the second in two days: on Saturday, Kirsty Coventry of Zimbabwe set the mark in the 200-meter backstroke. Coventry broke a record that had stood for 16 years.

"I was thinking about barbecue and no warm down," Coughlin said after the race. "I really didn't expect it."

Unlike most swim meets, the finals at the Missouri event are being held in the morning. The move is a concession to the schedule in the upcoming Beijing Olympics — and American TV viewers who will be able to follow the races live.

Earlier Sunday, Katie Hoff set her second American record in as many days when she and six-time Olympic gold medalist Michael Phelps each cruised to a pair of victories at the Missouri Grand Prix.

Both easily won their respective 200-meter freestyle and 400 individual medley races on the second day of the meet.

Hoff set an American record in the 200, finishing in 1 minute, 56.08 seconds to defeat Coughlin for the second time in two days. Coughlin set the previous mark.

On Saturday, Hoff broke the oldest American record on the books in the 400 freestyle. Hoff beat Coventry in Sunday's medley race.

The 18-year-old Hoff, the youngest U.S. Olympian four years ago, seems reluctant to embrace the role of America's top overall female swimmer heading toward the Beijing Olympics in six months.

"Everyone has something to bring," she said, naming several other top female swimmers. "I'm just excited to be confident going into the next five or six months of training and getting ready for (Olympic) trials."

With two events remaining on the final day of the Grand Prix on Monday, Hoff has won four races here.

Phelps, who also won the only event he entered Saturday, was disappointed with his time of 4 minutes, 14.08 seconds in the medley Sunday. While second-place finisher Thiago Pereira was more than four seconds back, Phelps' time was nearly eight seconds off his personal best, which is a world record.

"I'm not happy about the 400 IM and where it is right now," he said. "I just have to get back into swimming back-to-back events, and being able to swim them well."

Phelps, the undisputed face of American swimming and a contender to break Mark Spitz's record of seven gold medals in a single Olympics, said he isn't surprised by the ascension of Hoff, his former teammate at the North Baltimore Aquatic Club.

"Our club team has always had a tradition for excellence," said Phelps, who now lives and trains in Ann Arbor, Mich. "I have no idea what they put in the water (there), but obviously it's something good."

Joining Phelps and Hoff as multiple winners at the meet was Cesar Cielo of Brazil, who won the 50 freestyle in 22.01 seconds. Fred Bousquet finished second, 0.04 seconds behind.

Cielo, who trains in Atlanta and swam at Auburn, won the 100-meter freestyle Saturday.