SYDNEY - Juan Martin del Potro continued his promising return from an 11-month injury layoff by beating top-seeded Fabio Fognini 4-6, 6-2, 6-2 on Wednesday to reach the quarterfinals of the Sydney International.

The former fourth-ranked player from Argentina needed a wild-card entry to get into the main draw because his world ranking had dropped to 338 during his lengthy absence.

Second-seeded David Goffin of Belgium also lost, falling to Simone Bolelli of Italy 6-3, 6-3, while Bernard Tomic of Australia defeated third-seeded Philipp Kohlschreiber of Germany 6-3, 6-4.

Del Potro, the 2009 U.S. Open champion, needed treatment from the courtside trainer during the first set. He has said he still has wrist pain and his injury constrains his two-handed backhand.

The Argentine's quarterfinal opponent will be Kazakhstan qualifier Mikhail Kukushkin, who beat sixth-seeded Pablo Cuevas 7-5, 7-5.

On the women's side, defending champion Tsvetana Pironkova beat Barbora Zhalavova Strycova 6-4, 6-1 to stay on track to win the tournament for the second consecutive year as a qualifier.

Also winning a quarterfinal match was Wimbledon champion Petra Kvitova, who beat Jarmila Gajdosova 4-6, 6-3, 6-4.

At the Kooyong Classic in Melbourne, defending champion Kei Nishikori of Japan struggled in the first round before beating Australian youngster Jordan Thompson 6-4, 3-6, 7-6 (4).

Also, Fernando Verdasco of Spain beat Gilles Simon of France 6-2, 7-6 (3) and Alexandr Dolgopolov of Ukraine defeated Filip Krajinovic of Serbia 6-4, 6-3.

No play was possible at the WTA Tour's Hobart International because of rain.