Novak Djokovic survived a scare to join Roger Federer and Serena Williams in the Australian Open second round as heavy downpours caused chaos on Monday.
Defending champion Djokovic was made to sweat before beating Germany's Jan-Lennard Struff in four sets on the first day, when fears over air pollution were replaced by the disruption by rain.
While play continued at the three stadiums with retractable roofs, half of the 64 scheduled matches were postponed, ensuring a big backlog for Tuesday.
Wet conditions are unusual for the Australian Open, which is more used to extreme heat and was plagued by smog from bushfires during qualifying, when players suffered coughing fits and breathing problems.
World number three Federer was briefly hauled off court while the roof was closed on Rod Laver Arena before returning to complete a routine 6-3, 6-2, 6-2 victory over American Steve Johnson.
Williams, on the hunt for a record-equalling 24th Grand Slam title, won the first set against Anastasia Potapova in just 19 minutes as she cruised to a 6-0, 6-3 win in less than an hour.
"I feel like I can still improve and get better throughout this tournament, for sure. This is a good stepping stone for right now," Williams said.
However, Williams' elder sister Venus was ousted in stunning fashion by 15-year-old Coco Gauff, who won 7-6 (7/5), 6-3 in a repeat of her first-round upset at Wimbledon last year.
In the late match, defending champion Djokovic dropped his first set since 2006 in the opening round before recovering to beat Jan-Lennard Struff 7-6 (7/5), 6-2, 2-6, 6-1.
"There is a lot of pressure and a lot of different emotions involved. I definitely try to remind myself to stay present and really enjoy," said the seven-time Melbourne winner, who brought up his 900th Tour-level victory.
Former US Open champion Sloane Stephens was the biggest women's casualty on day one when she crashed out in three sets to Zhang Shuai of China - her fourth first-round exit in Melbourne. (AFP)