Second-seed Petra Kvitova suffered an upset 6-4, 6-3 loss to Bulgarian qualifier Tsvetana Pironkova in the semi-finals of the Sydney International.

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 108.

"First time into a WTA final - it's an amazing feeling,'' said the 26-year-old Pironkova.

"I've been waiting for this for a long time.''

With qualifiers and main draw, she has now won seven consecutive matches in Sydney and is aiming for an eighth 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 semi-final against Russia's Dmitry Tursunov.

Del Potro, the 2009 US Open champion who finished last season ranked fifth, relied on his strong serve, with 14 aces to three, and saved seven of 10 break points.

Tursunov had a 7-6, 6-2 win over Denis Istomin of Uzbekistan.

Isner through

John Isner reached the semifinals of the ATP's Heineken Open in Auckland after a 6-7, 7-6, 7-6 win over fifth-seeded Philipp Kohlschreiber in a match between former champions.

The quarter-final between third-seeded Isner, the 2010 Auckland champion, and No 22-ranked Kohlschreiber, the 2008 winner and beaten finalist last year, lasted two hours, 24 minutes and contained no breaks of serve.

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 semi-finals with a 6-3, 6-2 win over 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.

Source: Reuters