Li Na avenged her third-round loss to Laura Robson in last year's U.S. Open, winning their rematch at the same stage Friday.
The fifth-seeded Li rallied from down a break in the second set for a 6-2, 7-5 victory. In 2012, Li was seeded ninth, while Robson was ranked 89th. Now the British teen is seeded No. 30, but she was overmatched Friday.
Li, the 2011 French Open champ, had 11 aces and won all nine points when she went to the net.
The 19-year-old Robson was coming off a fourth-round run at Wimbledon. She made her breakthrough at last year's U.S. Open, beating Grand Slam winners Kim Clijsters and Li back-to-back.
But she had 30 unforced errors to seven winners on Friday.