Brisbane: Estonia's Kaia Kanepi provided the upset of the Brisbane International quarter-finals when she beat second seed and world number 10 Andrea Petkovic 6-1 7-6 on Thursday.

The hard-hitting Kanepi had been cruising to victory but needed five match points to seal the win as her German opponent offered some late resistance.

Petkovic had been hampered by a back injury throughout the match but was able to increase the pressure when the 26-year-old was serving for the match at 5-4 and eventually forced a tie-break.

Despite having an opportunity to finish off the match on three further occasions, Kanepi finally managed to seal the win 9-7 in the tie-break after one hour, 40 minutes to set up a semi-final against Francesca Schiavone.

Third seed Schiavone had earlier ground down former world number one Jelena Jankovic in a drawn-out quarter-final that lasted almost three hours as both players squandered numerous match point opportunities.

Jankovic wasted two match points in the second set, after winning the first, while the 2010 French Open champion Schiavone also squandered two match points of her own in the third set before she ran out a 5-7 7-6 6-3 winner.

Slovakia's Daniela Hantuchova had a walkover into the semi-finals after Serena Williams withdrew from the tournament with an ankle injury that she sustained in her second round victory over Serbia's Bojana Jovanovski.

Men's second seed Gilles Simon, started sluggishly but managed to overcome Santiago Giraldo 7-6 6-4 in the men's quarter-finals.

Simon, who beat American Ryan Sweeting and Australia's James Duckworth in the first two rounds, is building nicely for the Australian Open later this month in Melbourne, something the Frenchman was pleased with.

"I've already played three good matches so it's good preparation for Melbourne," Simon said.

"I'm feeling good, I'm moving better and better everyday."