SYDNEY (AP) -- Former U.S. Open champions Juan Martin del Potro and Samantha Stosur rallied to win their second-round matches against tough French opponents Wednesday at Australian Open warm-up tournaments.
Del Potro beat Nicolas Mahut 1-6, 6-3, 6-4 at the Sydney International, while Stosur saved two match points and eked out a 6-4, 2-6, 7-6 (7) win over Kristina Mladenovic at the Hobart International.
Stosur lost all three of her singles matches at the Hopman Cup team exhibition event last week and is looking for some confidence heading into her home Grand Slam at Melbourne Park, where she has never advanced past the fourth round.
''Any win's a good win, but when you've got to really tough it out and battle through a long match ... you're probably holding your nerve pretty well,'' Stosur said.
The Australian Open begins Monday.
Earlier, former Wimbledon champion Petra Kvitova advanced to the semifinals of the women's event in Sydney with a 7-6 (4), 6-2 victory over Lucie Safarova. Kvitova, the second seeded player, will play Tsvetana Pironkova in the semifinals after the Bulgarian's 7-6 (2), 6-3 win over Sara Errani.
In a late match, Madison Keys advanced to the semifinals when Bethanie Mattek-Sands retired with a lower back injury while trailing 3-2 in the first set. Mattek-Sands, who beat top-seeded Agnieszka Radwanska on Tuesday, said she still hoped to play in the Australian Open.
In other men's matches in Sydney, defending champion Bernard Tomic of Australia reached the quarterfinals with a 6-3, 4-6, 6-4 win over Blaz Kavcic of Slovenia, and Marinko Matosevic defeated third-seeded Andreas Seppi of Italy 6-3, 6-4.
Also, Alexandr Dolgopolov beat second-seeded Jerzy Janowicz of Poland 6-2, 6-2, Denis Istomin defeated No. 7 Marin Cilic 6-3, 6-4 and No. 4 Dmitry Tursunov defeated Lukas Rosol 3-6, 6-3, 6-3.
In Hobart, defending champion Elena Vesnina retired from her second-round match with a back injury. Spanish qualifier Estrella Cabeza Candela was leading the match 4-6, 6-2, 4-1 when Vesnina quit.
Also, second-seeded Kirsten Flipkens of Belgium beat wild-card entry Storm Sanders of Australia 4-6, 7-6 (3), 7-6 (5).
At the ATP's Heineken Open in Auckland, New Zealand, American wild-card entry Jack Sock pulled off the biggest win of his career when he beat second-seeded Tommy Hass 6-4, 6-4 in the second round.
The 21-year-old Sock is 14 years younger than Haas and his ranking is nearly 90 places lower than the 12th-ranked German. But Sock started strongly and got early breaks in both sets.
Sock will face Roberto Batista Agut in Thursday's quarterfinals after the Spaniard beat sixth-seeded Benoit Paire of France 6-3, 6-4.
David Ferrer, the No. 1-seeded player and defending champion, beat Donald Young of the United States 6-7 (5), 6-3, 6-1. The Spaniard is seeking his fifth Auckland singles title.
Third-seeded John Isner also progressed to the quarterfinals with a 7-6 (1), 3-6, 6-2 win over Lucas Lacko. Isner's participation in the tournament had been in doubt because of an ankle injury, but the American seemed fit in a match that lasted nearly two hours.
American qualifier Steve Johnson beat Marcos Baghdatis 7-5, 6-7 (3), 6-4 in a first-round match held over from Tuesday because of rain.
In the men's exhibition tournament in Kooyong, Tomas Berdych beat Fernando Verdasco 7-5, 6-2, and Stanislas Wawrinka defeated Gilles Simon 6-4, 5-7, 6-3.