Florida final for battling Serena

A match elongated by a mysterious lower back injury suffered by the American in the first set, plus a 10-minute heat break between the second and third ended when Williams broke in the penultimate game and then clung on to her serve.

Having won this tournament four times in her career - only one less than Steffi Graf, the event's most successful player in history - the younger Williams sibling expects to triumph here.

Scroll down for more

Battler: Williams made it through

If not her, then sister Venus, who has won it three times and was knocked out in the previous round by the feisty Russian.

While not as glamorous as her compatriot Maria Sharapova, Kuznetsova actually has a higher ranking and an intelligent game which sees her work opponents cleverly around the court.

For a while it seemed that she would become only the seventh player to beat the Williams sisters at the same tournament (and the only non-world number one to do so.)

The American was twice treated by the trainer in the first set, the first intervention coming after just the fifth game, but soon she was bounding around and staging a comeback.

In high humidity both players were exhausted, but after 167 minutes it was Williams, who lives up the coast and is used to the conditions, who lasted out the best.

Quietly and with little fuss Raphael Nadal has been shoring up his ranking this week by progressing to the semi-finals of the men's event, in which he meets Tomas Berdych of the Czech Republic.