LOS ANGELES -- Last summer, Australian teen-ager Jon Sieben swam at the Olympic pool on the Southern California campus and came away empty.
One year later, the Aussie swimmer is being hailed as the upset winner of the 1984 swimming competition after he defeated world record holder Michael Gross in the 200-meter butterfly in world record time Friday.
The Sieben show upstaged another banner gold medal day for American swimmers, who harvested four more golds and swelled their total to 18. That put the United States within range of its previous record haul of 21 in Mexico City in 1968.
Tracy Caulkins and Tiffany Cohen swam to golds in Olympic record setting time and Rick Carey captured the 200-backstroke. Caulkins also helped the medley relay team to the gold.
Gross, who won golds in world record time in the 200 free and 100-butterfly, lost his lead in the final 25 meters and settled for the silver, his fourth medal of the Olympics.
'We clipped his wings, the big fella,' said Australian Coach Laurie Lawrence, referring to the 6-foot-7 Gross. 'It's been fantastic. I knew Sieben could go good but I didn't realize he could get the world record. I'm out of my tree.'
Siben, who plans to attend Alabama, where U.S Olympic Coach Don Gambril is mentor, wasn't thinking victory.
'This morning, I was thinking of getting a medal, not about winning,' said Sieben, who finished with a fourth best time in the prelims. 'I didn't let anything bother me or worry me. I felt comfortable. There wasn't any pressure on me.'
Gross, whose world record time was only one-hundredth of a second slower than Sieben's mark of 1:57.04, hinted he might have been tired after swimming so many races.
'If this had been Tuesday, I think that I would have won easily, but I did not feel anywhere nearly as good as I did on Tuesday,' Gross said. 'Maybe I had too many races, maybe not. Oh well, it doesn't really matter that much.'
American Pablo Morales finished fourth, just behind bronze medalist Rafael Vidal of Venezuela.
Tracy Caulkins, America's reigning swimming queen, won her second Olympic gold medal sweeping the medley races. Caulkins set an Olympic and American record by racing to victory in the 200-meter individual medley.
'It was hard out there,' said Caulkins, clocked in 2:12.64, betting the 1972 Olympic mark of Shane Gould of Australia (the event hasn't been staged since then in the Olympics). 'I think I might have tried a little too hard and didn't relax.'
Caulkins, 21, winner of 48 national titles, trailed silver medalist Nancy Hogshead of the U.S. after the breastroke but grabbed the lead in the second 50 meters in the backstroke and never looked back in swimming the fourth fastest time in history. However, the Nashville, Tenn. swimmer's time was still off East Germany's Ute Geweniger's world best of 2:11.73.
Hogshead, who picked up her third and fourth medals Friday, has a shot at tying the Olympic women's personal mark of five medals set by Kornelia Ender of East Germany and American Shirley Babashoff in 1976.
Cohen, who won the 400-freestyle earlier in the week, flirted with the oldest record left on the swimming books -- Australian Tracey Wickham's 1978 mark of 8:24.62 -- before settling for a 8:24.95 clocking. Cohen was ahead of Wickham's pace until the final 100 meters.
'Three-tenths of a second, ahhhh!,' said the 18-year old Cohen. 'I really wanted to break the world record since this might be my last swimmer race ever and it would have been nice to finish with a world record.
Michele Richardson, at 15 the youngest member of the American Olympic team, won the silver.
Carey, criticized for not showing more emotion in winning the 200-backstroke, had hoped to break two world records at the Olympics. He settled for two golds instead with his :55.79 clocking in the 100-backstroke, off his world best and John Naber's 1976 Olympic mark.
'I wanted to win. I wanted to go 1-2 with this guy right here,' said Carey, pointing to American teammate David Wilson who captured the silver. 'My time wasn't that good but I don't care, I won.'
The American women kept the U.S. record intact in relay races by capturing the 400-medley relay. The Americans spotted the West Germans the early lead but world record holder Mary T. Meagher swam a :58.04 in her leg of the butterfly to put the quartet ahead to stay. Hogshead, swimming the freestyle anchor, stretched the win to a three-second victory over the West Germans.