China's top tennis player Li Na booked her place in the Sydney International semifinals, after a grueling marathon win over Russian Svetlana Kuznetsova on Wednesday.

Li returned to the Sydney semifinals for the first time since 2007, after out-lasting the two-time grand slam champion Kuznetsova with a 3-6, 7-6, 6-3 success coming after almost two-and-a-half hours.

The 11th-ranked Li will now play qualifier Bojana Jovanovski in Thursday's semifinals after the Serbian defeated Italian Flavia Pennetta 6-4, 6-1.

Li made the Australian Open semis last year as she became the first Chinese player to make the world's top 10, and she is hoping for another good showing at Melbourne after challenging for the Sydney title.

It was Li's fourth win against the former French and U.S. Open champion Kuznetsova in their 11 meetings, and she was pleased to have got past Kuznetsova.

"It was a tough match because the conditions were hot today," Li told ABC Sports on Wednesday.

"It is always tough when we play each other. We have played many times.

"We didn't want to play a long match, but every time we play it's long. We know each other pretty well and sometimes we practice together, so we know how each other plays on the court."