Jankovic is currently ranked ninth in the world

Williams won four games in a row to take the opening set but lost a scrappy second after the Serbian second seed broke decisively in the eighth game.

Jankovic took the match with a winner that needed to be checked by the umpire after a topsy-turvy tie-break.

She now faces fourth seed Dinara Safina after Vera Zvonareva retired in their semi-final with the score at 6-3 0-1.

The all-Russian encounter was ended when Zvonareva decided not to risk further damage to a wrist injury.

"It just got really bad to the point I wasn't able to perform," she said.

It was the second match in a row Safina's opponent has retired.

Tatiana Golovin of France retired from their match on Friday at the end of the first set with an injured ankle.