Juan Martin del Potro into quarters

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.

Heineken Open: A high rate of attrition among seeded players has continued in Auckland. Fifth seed Tommy Robredo of Spain on Wednesday became the fourth seeded player to withdraw from the tournament without hitting a ball.

World No. 17 Robredo, who had a first round bye, pulled out of his second round match against New Zealand's Michael Vensu with a hip injury, saying there was a "little bit" of doubt about his fitness for the Australian Open.

"I arrived here on Friday, my intention was to play here and prepare myself for a great tournament," Robredo said. "Two days ago I was in the gym working hard and then practicing and suddenly I felt something in my adductor (muscle).

"I have been one and a half days without practice and trying to recover to play here but I'm not ready to play a match."

Robredo's withdrawal follows those of top seed David Ferrer and defending champion John Isner, both citing tiredness, and Frenchman Gael Monfils, for personal reasons.

On court, second seed Ernests Gulbis of Latvia lost 2-6, 6-3, 6-1 to qualifier Jiri Veseley of the Czech Republic while third seed Robert Bautista Agut of Spain retired while trailing France's Adrian Mannarino 6-4, 2-1 in his second round match with an unspecified injury.

Sixth seed Santiago Giraldo of Colombia and seventh seed Guillermo Garcia-Lopez of Spain were both beaten in the first round.

Fourth-seeded South African Kevin Anderson bucked the trend against seeds when he beat Germany's Jan-Lennard Struff 7-6 (6), 6-1.

"I felt I returned really well today," Anderson said. "I was pleased with the way I hit my backhand.

"My opponent hit the big ball and didn't give me a lot of time so I thought I played defense well too."

Eighth seed Steve Johnson of the United States also reached the quarterfinals, beating Pablo Carreno Busta of Spain 6-7 (3), 6-4, 6-1.

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.

Hobert International: No play was possible at the WTA Tour event because of rain.