By Zjan Shirinian

A fan covers himself from the heat with a towel during the match between Maria Sharapova and Karin Knapp ©Getty ImagesJanuary 16 - Play was suspended for more than four hours on all but two of the courts in Melbourne during another scorching day at the Australian Open, as the "extreme heat policy" was finally implemented.

With temperatures soaring past 43 degrees Celcius for the first time since the tournament began on Monday (January 13), referee Wayne McKewen decided it was too hot for play to continue on the open courts.

But the decision was too late for four-times Grand Slam champion Maria Sharapova, who was already into a final set against Karin Knapp of Italy.

Under tournament rules, any set already started on Rod Laver Arena and Hisense Arena must be completed before the roofs can be brought across to shield players and spectators from the heat.

The pair played for more than an hour once the heat policy was implemented, before Russian Sharapova won the second round tie 6-3, 4-6, 10-8 in a three-and-a-half hour epic.

Sharapova wrapped herself in ice towels between points.

SharapovaMaria Sharapova cools off during a break in her match against Karin Knapp ©GettyImages

Belgian Kirsten Flipkens, a semi-finalist at Wimbledon last year, tweeted: "FINALLY!!!! Play suspended because of the heat... Heat policy should have been in two days ago already... #burning #crazy #nothealthy."

On the men's side of the draw, number one seed Rafael Nadal won in straight sets over Australian Thanasi Kokkinakis.

The Spaniard came out on top 6-2, 6-4, 6-2 in their second round encounter.

Swiss Roger Federer also beat Blaz Kavcic of Slovenia in straight sets, 6-2, 6-1, 7-6.

The big upset of the day came in the match involving fifth seed Juan Martin del Potro.

The Argentine lost in five sets to Roberto Bautista Agut, of Spain, 4-6, 6-3, 5-7, 6-4, 7-5.

Three-times Australian Open finalist Andy Murray, of Great Britain, beat Frenchman Vincent Millot 6-2, 6-2, 7-5 in the final match on Rod Laver Arena.