Kim Clijsters (4/1 Tournament Outright) has admitted her concerns over the heat at the Australian Open but still kept her title defence on track with an impressive win over outgoing world number one Caroline Wozniacki, coming through in straight sets 6-3 7-6 (7-4).

The Belgian showed no signs of the ankle injury picked up in her marathon fourth-round clash with Li Na as her power from the baseline put her on the verge of victory, going a set and 5-2 in front.

However, Wozniacki – who has spent 67 of the last 68 weeks as the top-ranked female player – fought back to force a tie-break in the second set.

The Dane, who has yet to win a Grand Slam event, seemed to struggle for gas when it mattered as Clijsters regained her rhythm to book her semi-final place.

“It definitely didn’t feel like I was up a set and 5-2, Caroline is a very consistent player and a fighter and she became more aggressive,” said Clijsters.

“I am happy to get through and not have to go to a three-setter as it’s so hot.”

Wozniacki will now no longer be the world number one while Clijsters will face third seed Victoria Azarenka – who has a chance of rising to the top – in the last four after the Belarusian (5/2 Tournament Outright) beat Agnieszka Radwanska 6-7 (0-7) 6-0 6-2.