Melbourne - An Australian Open hit by weather extremes faced a new challenge on Thursday: dirty rain, as overnight downpours left courts muddy and unplayable.
Workers armed with squeegees and high-pressure hoses rushed to clean the surfaces, delaying some matches for several hours.
The dirty rain, the result of dust storms becoming caught up in a cold front, coated cars with orange mud, forced public pools to close and turned Melbourne's Yarra River brown.
It also plastered Melbourne Park, the tennis venue on the banks of the Yarra, further disrupting a tournament that has already weathered bushfire smoke, torrential rain and wind.
"Due to the rain and dust overnight the outside courts need high-pressure cleaning," organisers tweeted.
"Our team is working across Melbourne Park to prepare the outside courts for play."
Further rain set back Thursday's action yet more, with some courts out of action five hours after the scheduled start on day four.
Weather conditions have been a major talking point at the Australian Open after smog from deadly wildfires hit hazardous levels during qualifying last week, leaving players with coughing fits and breathing problems.
Although the haze cleared before the tournament's start on Monday it was replaced by torrential rain, which wiped out half of the day's schedule and caused a backlog of matches.
Strong breezes then buffeted Melbourne Park on Wednesday, giving players more problems as balls blew off-course and wobbled in the air.
The year's opening Grand Slam is traditionally plagued by a different kind of weather problem: extreme heat, which causes players to swathe themselves in ice towels and occasionally halts matches.
Switzerland's Belinda Bencic was among the few who played on schedule on Thursday, as she beat Jelena Ostapenko on Margaret Court Arena, one of three stadiums with a retractable roof.
"I'm super-happy to get the match out of the way. I didn't know the (other) courts were, like, wet and dirty and all that. But for sure it was difficult today," Bencic said.
"It was sometimes sunny and then suddenly was almost raining. Then windy. You just kind of have to accept it and go with it and try your best."
Men's champion Novak Djokovic, after contending with strong winds in his second-round win on Wednesday, said it was anyone's guess what the weather would serve up next.
"I don't know, you tell me," he said. "It's never pleasant to play in these kind of conditions when you have such a strong wind. Hopefully we won't be affected here in Melbourne by the quality of air."
Melbourne, on Australia's southern coast, has a well-earned reputation for changeable weather, prone to both cold Antarctic winds blowing across the Southern Ocean and hot Outback breezes.
Extreme weather is a growing concern in Australia after the bushfire emergency of recent months, which has left 29 dead and ravaged vast swathes of the country, torching thousands of homes.
Due to the rain and dust overnight the outside courts need high pressure cleaning, which is currently underway. Start of play has been delayed until midday. Updates to come.— #AusOpen (@AustralianOpen) January 23, 2020