NEW YORK, USA (AFP) — Defending champions Novak Djokovic and Samantha Stosur advanced in straight sets yesterday at the US Open, while British teen Laura Robson sent Li Na home after sending Kim Clijsters into retirement.

Serbian second seed Djokovic overwhelmed Brazil's Rogerio Dutra Silva 6-2, 6-1, 6-2, never facing a break point and winning 90 per cent of his first-serve points to reach the last 32 in 99 minutes on the Flushing Meadows hardcourts.

Next for Djokovic will be either France's Julien Benneteau or Russian-born US teen Dennis Novikov, the lowest-ranked player ever in the second round of a Grand Slam event at 1,098th.

British teen Laura Robson ousted Chinese ninth seed and 2011 French Open winner Li 6-4, 6-7 (5/7), 6-2 for her first career triumph over a top-10 foe, booking a fourth-round showdown against Australian seventh seed Stosur.

Robson, an 18-year-old left-hander who was born in Australia but moved to Britain at age six, ended the career of three-time US Open champion Clijsters with a second-round triumph.

Robson, the youngest player in the world top 100 at 89th, became the first British woman in the fourth round of a Grand Slam since Sam Smith at Wimbledon in 1998, and the first in the Open's last 16 since Jo Durie in 1991.

Li did not reach the last eight at any Grand Slam tournament for the first season since 2008.

Stosur, who has not won a title since lifting the US Open trophy last year, took a 7-6 (7/5), 6-2 victory over US 31st seed Varvara Lepchenko and looked forward to the challenge Robson presents.

After fighting to 5-5 in the tie-breaker, Lepchenko sent a lob and a backhand wide to surrender the opening set after 59 minutes. Stosur broke in the third and fifth games of the second set and held to finish in 88 minutes.

"As the match went on I got a little more comfortable and relaxed a little bit more," Stosur said. "In the first set I felt like I served really well. That's how I was able to get into those games in the second set."

Spanish fourth seed David Ferrer moved into the third round by ousting Dutch qualifier Igor Sijsling 6-2, 6-3, 7-6 (14/12).

Ferrer, a 2007 US Open semi-finalist in his best Grand Slam run, battled to his sixth match point before Sijsling netted a forehand to finally fall.

Czech fifth seed Petra Kvitova ousted Pauline Parmentier 6-4, 6-4 to reach a round-of-16 match against her third consecutive French foe, 11th seed Marion Bartoli, who downed compatriot Kristina Mladenovic 6-2, 6-4.

Andy Roddick, the 2003 US Open champion who announced Thursday that this would be the final event of his career, will try to keep his career going into the weekend, the US 20th seed facing Australian Bernard Tomic.

Third-seeded Russian Maria Sharapova, the reigning French Open champion, meets US wild card Mallory Burdette and Belarus top seed Victoria Azarenka, the reigning Australian Open champion, plays China's Zheng Jie in later matches.