Despite making 39 unforced errors, the fourth seed prevailed in just over two hours against the second seeded Serbian, who has yet to win a grand slam title.

Williams struggled with unforced errors early on, dropping her second service game of the match to love and she looked set to go 3-1 down when Jankovic went 40-0 up in the next game.

But the fourth seed battled back, winning the next five points to break the Serbian and claimed another break on Jankovic's next service game as she moved into a 5-2 lead.

Serving for the set at 5-3, Williams put herself into a 0-40 hole and surrendered the game after saving two break points. But she had the Serbian into the same position in the next game and claimed the opening set 6-4 when Jankovic put her return on the second set point long.

Jankovic appeared out of sorts at the start of the second set and faced two break points in her first service game before holding for 1-1.

After five breaks of service in the opening set, the first six games of the second set went according to serve until Williams put a lazy drop shot from the baseline into the net to give Jankovic a 4-3 advantage.

The Serbian had a chance to close out the set when she went 40-0 up in Williams' next service game but the American held and broke Jankovic in the next game to make it 5-5.

Williams held to make it 6-5 and then took the match by breaking Jankovic with her 44th winner of the match.