Australian Open Day 4 : Tennis stars went to 3rd round through Melbourne Hot Weather.

Source: SBS

With a top of 39.1 degrees in the afternoon, day four turned out to be a challenging one for tennis players - and supporters.

Officials have been criticised for not suspending the games.

But the tournament´s ´Extreme Heat Policy´ only comes into effect when the temperature reaches 40C away from the heat of a court surface and the wet bulb globe temperature (which takes into account humidity) exceeds 32.5.

But the worst is still to come: Friday is expected to be another hotter-than-usual day, with a top of 42 degrees.

Maria Sharapova with ice bags in Melbourne Hot Weather Source: AFP

Last year's winner Roger Federer, who played later in the day, overcame Germany´s Jan-Lennard Struff, while fellow Swiss Stan Wawrinka was sent home by underdog Tennys Sandgren (US).

Stan is the first former Melbourne champion to leave the tournament prematurely this year.

In the Women´s draw, reigning Wimbledon champion Garbine Muguruza was the most prominent victim on day four. She lost to Taipei´s Su-Wei Hsieh in straight sets.

Maria Sharapova is still cruising comfortably through the tournament, beating Latvian Anastasija Sevastova in her second round.

The Russian, who took home the trophy in 2008, will now face 2016 champion Angelique Kerber in what is expected to be an exciting round-three clash this Saturday.

Before that, the German celebrated her 30th birthday with a win over Donna Vekic (CRO) - and some cake:

Angelique Kerber celebrated her 30th birthday

MELBOURNE, AUSTRALIA - JANUARY 18: Angelique Kerber of Germany was presented with a celebratory 30th birthday cake at Melbourne Park on January 18, 2018 Source: Getty Images

Here is the game summary in day 4.