Stosur, del Potro advance after tough wins

   
In other men's matches at Sydney, Australian wild card Marinko Matosevic upset third-seeded Andreas Seppi of Italy 6-3, 6-4 to reach the quarterfinals. Defending champion Bernard Tomic was scheduled to play his second-round match later Wednesday.
   
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.
   
At the ATP's Heineken Open in Auckland, New Zealand, American wild card Jack Sock got 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 to pull off the upset.
   
Sock will face Roberto Batista Agut in Thursday's quarterfinals after the Spaniard beat sixth-seeded Benoit Paire of France 6-3, 6-4.
   
Third-seeded American John Isner also progressed to the quarterfinals with a 7-6 (1), 3-6, 6-2 win over Lucas Lacko of Slovakia. Isner's participation in the tournament had been in doubt because of an ankle injury, but he seemed fit in a match that lasted nearly two hours.
   
American qualifier Steve Johnson beat Cypriot 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 at Kooyong, Tomas Berdych, the No. 7-ranked Czech, beat Spain's Fernando Verdasco 7-5, 6-2.