Ivanovic has suffered with a number of injuries since winning the French Open

Ana Ivanovic's poor run of form continued as she lost to Zheng Jie in the quarter-finals of the China Open.

The Serbian has struggled since winning the French Open in June and she slipped to a 7-6 (7-4) 2-6 6-4 defeat.

Zheng will play Svetlana Kuznetsova in Saturday's semi-finals after she beat Dominika Cibulkova 6-2 6-4.

In the men's quarter-finals, the unseeded Bjorn Phau knocked out reigning champion Fernando Gonzalez with a 6-3 4-6 6-3 victory.

Dudi Sela of Israel will join the German in the semi-finals after upsetting Tommy Robredo 6-4 6-1, while Rainer Schuettler also progressed after beating fourth seed Richard Gasquet 4-6 6-3 6-4.

The remaining last four spot will go to either Andy Roddick or Juan Carlos Ferrero, who are yet to contest their quarter-final match.

606: DEBATE It just seems at the moment that Ivanovic cannot sustain her game under pressure duggietoo

Zheng, who reached this year's Wimbledon semi-finals - beating Ivanovic en-route - was cheered on by a noisy home crowd and she was delighted with the win.

"This is a good win for me," she said. "It was in China and in front of my home crowd. There were lots of fans supporting me, which gave me even more motivation."

Ivanovic said: "I haven't had many matches in the last three months.

"Since the French Open, you can count them on one hand the number of matches I played.

"I've been really struggling with injuries and it was a very frustrating time. But now I am confident again that I play 100 per cent - and I can go on the court and work 100 per cent."