Roger Federer has been the unrivalled star of this Australian Open - but his wife, Mirka, did her best to steal the spotlight on semifinal night with an eye-catching sweater.

As Federer kept his hopes of winning a historic 18th grand slam title alive with a five-set win against compatriot Stan Wawrinka, Mirka sparkled on the sidelines in a Gucci number.

The bright pink pullover with green trim featured a roaring tiger print and the message L' Aveugle Par Amour (French for Blinded by Love). It created quite the storm on social media.

World No. 17 Federer looked two different players throughout the semifinal, blitzing the first two sets but then dropping the next two to his opponent in a bizarre drop in performance.

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Wawrinka continued the fight deep into the fifth set despite a nagging knee injury, but a late break from Federer was all he needed to get the upper hand and blast his way through to the finish line.

Federer reflected on the tough win after the match, admitting he thought he had it sealed in the third set.

"Honestly I thought I was in the match at the beginning of the third," he told Jim Courier after the match.

"Stan was playing with nothing to lose, I am not sure but it was very tricky to get to playing good tennis for both of us in the fifth set.

"I never ever thought in my wildest dreams that I would be coming this far here. It's beautiful. I am so happy."