Defending champion Angelique Kerber and top-seeded Andy Murray play their second-round matches on Wednesday in much more pleasant temperatures at Melbourne Park.
A cool change hit the city overnight, dropping temperatures from the 38 Celsius (100 Fahrenheit) on Tuesday afternoon to about 20 Celsius (68 Fahrenheit) when play began Wednesday.
Venus Williams was first up on Rod Laver Arena, playing Stefanie Voegele of Switzerland. Kerber was to follow against fellow German Carina Witthoeft, followed by Roger Federer against American qualifier Noah Rubin.
Murray was scheduled to play the last match on Wednesday night at Rod Laver.
Venus and Serena Williams were scheduled to play their opening doubles match on Wednesday afternoon.