Serena Williams says she may not have been able to play in the Australian Open had it not been pushed back by three weeks.
The first Grand Slam of the year was delayed to allow players to quarantine.
Williams, chasing a record-equalling 24th major singles title next week, said she "needed the extra time" to fully recover from an Achilles injury sustained at the US Open in September.
She and Britain's Katie Boulter won their openers as warm-up events began.
The two are playing in the Gippsland Trophy - one of six events running simultaneously at Melbourne Park this week to allow players to prepare for the Australian Open.
Boulter, playing in just her second WTA main draw match since February 2019, beat Russia's Anna Kalinskaya 6-1 6-3.
Williams claimed a a 6-1 6-4 victory over Australia's Daria Gavrilova.
"I don't think I would have been here if it was during the regular season," the 39-year-old American said.
"Achilles are like the worst thing, honestly. Oh my goodness, I didn't realise it would be this long.
"I definitely was pushing the limits, but I'm here."
The fifth seed will play Bulgaria's Tsvetana Pironkova in the last 16.
Boulter impresses on return to action
Boulter's 2019 season was cut short by a back injury which she sustained at the Fed Cup in April.
She played just two WTA main-draw matches in 2020, winning the first before being forced to retire against Sofia Kenin in the second round.
However, the 24-year-old needed just 59 minutes to beat Kalinskaya in Melbourne and set up a second round meeting with teenager Gauff.
American Gauff, who reached the fourth round of the Australian Open in 2020, battled past Switzerland's Jil Teichmann 6-3 6-7 (6-8) 7-6 (7-5).
Gauff squandered a 4-2 lead in the second set and a 4-1 advantage in the third before eventually winning in two hours and 47 minutes.
British number one Johanna Konta, who had a first-round bye, will play America's Bernarda Pera.
US Open champion Naomi Osaka and world number two Simona Halep are also in the main draw at this event.
Top seed Halep advanced to the third round with a 6-4 6-4 win over Russia's Anastasia Potapova.
In the Yarra Valley Classic, Britain's Francesca Jones lost 6-1 6-3 to French Open semi-finalist Nadia Podoroska of Argentina.
Venus Williams breezed past Arantxa Rus 6-1 6-3 to set up a second-round meeting with two-time Wimbledon champion Petra Kvitova.
World number one Ashleigh Barty will return to action on Tuesday against Ana Bogdan.
Australia's Barty, who chose not to travel in 2020 because of the pandemic, is joined in the main draw by Karolina Pliskova and Sofia Kenin.
In the men's Murray River Open, British number two Cameron Norrie was edged out 4-6 7-6 (7-2) 6-3 by American Tommy Paul.
Compatriot Dan Evans will play Pedro Sousa of Portugal in the same event on Tuesday.
The ATP Cup, a men's team event featuring world number one Novak Djokovic and 20-time Grand Slam champion Rafael Nadal, begins at Melbourne Park on Tuesday, while there is also a women's singles event - the Grampians Trophy - starting on Wednesday which is for players who have been in 'hard' quarantine.
All players arriving in Australia had to undergo a 14-day quarantine before the tournaments began. Most were able to leave their accommodation for five hours a day to train but a group of 72 were confined to their hotel rooms for the duration because of positive coronavirus cases on their charter flights.
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