French Open champion Li Na was upset in the first round of the U.S. Open by 53rd-ranked teenager Simona Halep.

Li, seeded sixth, lost 6-2, 7-5 on Tuesday. The second round at Flushing Meadows will be without all three of this year's major champions. Australian Open winner Kim Clijsters withdrew because of injury, while Wimbledon champ Petra Kvitova lost Monday. It's the first time that's happened since 1971.

Since Roland Garros, Li had not won consecutive matches until last week, when she reached the semifinals at New Haven.

The 19-year-old Halep beat a top-10 player for the first time in four tries. The Romanian was playing in her second U.S. Open match.

The match ended on Li's 54th unforced error.