For his 20th birthday Monday, U.S. swimmer Troy Dalbey, who recently enrolled at BYU, got to see a world-record performance. Unfortunately for both Dalbey and for his U.S. teammate Matt Biondi, the performance wasn't by either of them.

Dalbey and Biondi had poolside seats as Duncan Armstrong, an unheralded swimmer from Australia, won the Olympic gold medal in the 200-meter freestyle event with a world-record time of 1:47.25.Armstrong wasn't expected to be a factor in the much-talked-about final that featured Biondi, the world-record holder at 100 meters; Michael Gross of West Germany, the defending Olympic champion and holder of the world record going into the meet (at 1:47.44); and Dalbey, who gave Biondi all he could handle in the freestyle sprints at the U.S. Trials and was considered the likeliest darhorse.

But the Australian used a strong kick over the last 25 meters to touch the wall first and blow away all contenders.

Biondi finished third, Gross fifth and Dalbey seventh.

Dalbey had qualified for the eight-man final with a 1:48.96 heat time on Sunday. As the fifth-fastest qualifier he drew the second lane, next to Gross. Biondi was three lanes away and Armstrong four.

After the first 50 meters in the Olympic Park pool, Dalbey was in second place, trailing Steffen Zesner of East Germany. He maintained that position through 100 meters but then faded to sixth place at 150 meters and lost one more position over the final 50 meters.

His final time of 1:48.86 was slightly better than his qualifying time of 1:48.96 but slightly off the 1:48.35 he clocked at the U.S. Trials.

The race did serve as a portender of things to come - for both Armstrong and Dalbey. With the exception of Anders Holwertz of Sweden, they were the youngest swimmers in the race. Gross, at 24, and Biondi, who will be 23 in three weeks, are at the closing end of their sprinting careers.

Finishing seventh in the Olympics reflected a significant improvement for Dalbey, who ranked 16th in the world at 200 meters last year.

Dalbey will next compete in the 100-meter freestyle and with the U.S. freestyle relay team.