Valrico's Beth Bauer, the Duke star who won the Women's North and South Amateur last week at Pinehurst No. 2, bogeyed the final hole and lost to Candie Kung on Wednesday in the 99th U.S. Women's Amateur Championship.
Bauer, ranked second in the nation, missed several short putts and never led.
"I was on an adrenaline high the whole time on the back nine there. I thought I might be able to pull it out down the stretch, but I hit a poor iron shot at 18," Bauer said.
Kellee Booth, a former Arizona State star and the nation's top-ranked amateur who is expected to turn pro after this event, advanced to the round of 16 for the fourth time in the past six years.
She was two holes down after two holes in her opening match at 6,202-yard Biltmore Forest Country Club before beating Kareen Qually of Canada 6 and 5.
In her afternoon match, Booth, from Coto De Caza, Calif., was down three at the turn, but parred the final nine holes to beat Martina Eberl of Germany 1-up. Eberl had four bogeys on the back side.
Natalie Gulbis, 16, who shot 66 Tuesday en route to her record-setting medalist performance, struggled in her opening match, winning in 20 holes against Laura Torrisi of Lunenburg, Mass.
Gulbis was three down after six holes and was never more than 1-up in the match, which went to extra holes when the high school senior from California chunked a chip shot from the fairway then hit her approach shot in a bunker.
Gulbis won on the 20th hole with a 10-foot par putt. But in the afternoon, Gulbis lost 1-up to Mayumi Nakajima.
The most impressive day was turned in by Lorena Ochoa of Mexico, who won her opening match 7 and 6 over Kathryn Cusick of Jacksonville, and came back in the afternoon with a 6-and-5 victory over Celeste Troche of Paraguay.
Ochoa, who shot 3-under-par 69 in Tuesday's second day of stroke-play qualifying, had five birdies in her first match and three in her second.
Thirty-six holes of match play are scheduled today and 18-hole semifinal matches are Friday. The finalists play 36 holes Saturday for the championship.