SYDNEY — Second-seeded Petra Kvitova suffered an upset 6-4, 6-3 loss to Bulgarian qualifier Tsvetana Pironkova in the semifinals of the Sydney International today.
Kvitova, the 2011 Wimbledon champion, was broken twice in the first set and four times in the second against Pironkova, who finished last season ranked No. 108.
With qualifiers and main draw, she has now won seven consecutive matches in Sydney and is aiming for No. 8 in the final, where she'll meet either fifth-seeded Angelique Kerber or American Madison Keys.
Men's top seed Juan Martin del Potro beat Czech veteran Radek Stepanek 6-4, 3-6, 6-3 to set up a semifinal against Russia's Dmitry Tursunov.
Del Potro, the 2009 U.S. Open champion who finished last season ranked No. 5, relied on his strong serve, with 14 aces to three, and saved seven of 10 break points.
Tursunov had a 7-6 (5), 6-2 win over Denis Istomin of Uzbekistan. Defending champion Bernard Tomic was playing Alexandr Dolgopolov of Ukraine in a later quarterfinal.
John Isner reached the semifinals of the ATP's Heineken Open in Auckland, New Zealand after a 6-7 (4), 7-6 (4), 7-6 (5) win over fifth-seeded Philipp Kohlschreiber in a match between former champions.
The quarterfinal match between third-seeded Isner, the 2010 Auckland champion, and No. 22-ranked Kohlschreiber, the 2008 winner and beaten finalist last year, lasted 2 hours, 24 minutes and contained no breaks of serve.
Playing on an injured ankle, Isner finally clinched the match with a vital point against serve in the third-set tiebreak.
Isner served 18 aces, put 83 percent of first serves in play and won 82 percent of first serve points.
Isner will next play Spain's Roberto Bautista Agut, who beat American wildcard entry Jack Sock 6-1, 6-3 in a rain-interupted match.
In the WTA event at Hobart, top-seeded Sam Stosur reached the semifinals with a 6-3, 6-2 win over No. 34-ranked Bojana Jovanovski of Serbia.
The 2011 U.S. Open champion next faces seventh-seeded Klara Zakopalova of the Czech Republic, who beat American Alison Riske 6-4, 7-5.
In the exhibition tournament at Kooyong, the former Australian Open venue in Melbourne, No. 7-ranked Tomas Berdych advanced to the final with a 6-4, 6-1 win over Kei Nishikori of Japan.