China's Li Na said she was playing her best tennis since before last year's Wimbledon as she battled into the semi-finals of the Sydney International on Wednesday. The world number five needed 1hr 50min to subdue fighting Czech Lucie Safarova 6-2, 7-6 (7/3) in blustery conditions to move into the last four in the defence of the Sydney title she won last year. It was Li's third win this week, continuing her upsurge in form after a dismal follow-up to her landmark French Open success at Roland Garros, which saw her become the first Asian to win a grand slam title. She now faces either world number two Petra Kvitova or Slovakia's Daniela Hantuchova in Thursday's semi-finals, while world number one Caroline Wozniacki was due to face Polish seventh seed Agnieszka Radwanska later Wednesday. Third seed Victoria Azarenka was playing France's Marion Bartoli in the other quarter-final. Li, 29, was clearly relieved to have put her problems of the second half of 2011 behind her and eyeing back-to-back Sydney finals. "Of course I'm feeling good," she said. "Win here last year and this year reach the semis in just the beginning of the year, yeah, I am feeling much, much stronger." Li, who only won seven matches after her French Open breakthrough, said she was back in the form prior to Wimbledon when she bowed out to Germany's Sabine Lisicki in the second round. "Last year before Wimbledon," Li said, when asked the last time she was playing at this level. "I mean, even in Wimbledon I was feeling I was playing well. But after that I don't know what happened. Didn't work." Li said she was thankful that her match with world number 25 Safarova did not go to a third set. "I was feeling my hand at the beginning of the tiebreak. I was so lucky I won the tiebreak," she said. "If not, I think for sure I would lose the third set, because she was trying so hard on the court and was playing better and better. I just pushed the ball back to the court."