Defending champion Andy Murray's joined Novak Djokovic in the third round of the US tennis Open but the Scot dropped the third set to Argentina's Leonardo Mayer before winning 7-5 6-1 3-6 6-1.
Djokovic had to overcome an early wobble, the world number seeing off two set points before beating German Benjamin Becker 7-6 6-2 6-2.
China's Li Na is the first player to reach the round of 16, avenging last year's loss to Britain's Laura Robson in straight sets in just 81 minutes
Also progressing were third seed Agnieszka Radwanska of Poland, fifth-seeded Czech Tomas Berdych and German 12th seed Tommy Haas.
New Zealand number one Marina Erakovic reached the third round of the doubles with Zimbabwean partner Cara Black, the 13th seeds beating an American/Chinese combination in straight sets.