Can Roger Federer cause an upset against Novak Djokovic in Melbourne?

The two stars meet for the 45th time in their careers this morning

tennis, djokovic, federer, australian open

Novak Djokovic and Roger Federer before last year's US Open Final (AP Photo/Julio Cortez)

Novak Djokovic and Roger Federer renew their rivalry for a 45th time later this morning with both men having won 22 of their previous 44 clashes.

The two men meet in the semi-finals of the Australian Open with a place for the winner against either Andy Murray of Milos Raonic in the final. Djokovic and Federer last met in a Grand Slam at last year's US Open final where the Serbian star won in New York in four sets. 

On last night's Off the Ball, tennis journalist Sean Calvert said that despite Djokovic winning five of the last six Grand Slam matches, Federer has a chance to win is he plays "almost flawless tennis".

"Djokovic has been very mediocre by his own very high standards" in the tournament so far. The World Number 1 has only lost two sets in the tournament but was taken to five sets by France's Gilles Simon in the Fourth Round.

Calvert claims that the Melbourne conditions would suit Federer over a shorter match but in Grand Slam conditions, Djokovic's durability is key. "It's very difficult to play the kind of tennis to beat Djokovic and keep it up over five sets."

Murray and Raonic play tomorrow in the second semi-final and Calvert added that Raonic "has more of a chance of beating Murray that perhaps Federer has (against Djokovic) in this best-of-five format.