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