The American, however, apparently injured herself during a 6-3, 6-3 win over another Russian, world No. 11 Elena Dementieva.

A trainer massaged her back during the match. Williams said after the match she wasn't sure about the nature of the injury — she said she thought she hurt her hamstring but the trainer suspected the discomfort originated from her back.

Williams also said she was worried about re-injuring her left wrist but said it was currently healthy.

"It was really strange. I was able to get through the match even though she (Dementieva) was playing really well," Williams said of her new injury.

Dementieva played inconsistently after upsetting world No. 4, Serbian Ana Ivanovic, in the quarterfinals.

She double faulted and missed a forehand and a backhand in the final game to give Williams the break and the match.

Sharapova beat Russian compatriot Anna Chakvetadze 6-4, 6-2 in the other semifinal.

Both players struggled at first, dropping their opening two service games. Sharapova finally held in the sixth game to give her a 4-2 lead from where she took the opening set.

World No. 6 Chakvetadze double-faulted to help give Sharapova breaks in the first and seventh games of the second set and a 5-2 lead. Sharapova held again to take the match.

"I was a little slow at the beginning, definitely, but the good thing is that I recovered from that," Sharapova said, adding that she took chances on some second serves.

The form of Sharapova, Chakvetadze and Dementieva in the lead-up to the Australian Open — beginning Jan. 14 — showed the Russian threat would be strong in Melbourne.

Sharapova said the number of Russians in the top echelons of women's tennis was remarkable because they all trained in different places — instead of emerging from a single program.