Double defending champion Jannik Sinner advanced to the second round of the Australian Open on Tuesday in just over an hour of tennis after his French opponent Hugo Gaston retired upon losing the first two sets 6-2, 6-1.

In his first official match since beating Carlos Alcaraz for the ATP Finals crown, the Italian world number two was in ominous form on the Rod Laver Arena court he has ruled for two years before the match was cut short.

After losing the second set, Gaston gestured he could no longer continue and retired to his seat to cry under a towel.

Sinner said he was surprised by the retirement but could see Gaston was not at his best.

Sinner will continue his bid for a third successive Australian Open crown against the winner of James Duckworth and Dino Prizmic.

Meanwhile, showman Gael Monfils bowed out of his 20th and final Australian Open with a mix of pain and regret as he fell to an injury-hampered 6-7(3), 7-5, 6-4, 7-5 defeat in the first round to local qualifier Dane Sweeny.

The 39-year-old Frenchman had flashes of his trademark flamboyance and somehow made a game of it despite being severely restricted in his movement amid a heady atmosphere at Kia Arena.

"My journey started in 2003 with you guys, now we are in 2026 and somehow it's the finish line. Thank you so much for this amazing ride, you guys have been unbelievable," Monfils told the cheering fans who gave him a standing ovation.

"I've got a lot of great memories here ... I've been very lucky to play here for many years. Thank you very much."

Home fans, some toting inflatable kangaroos, were in full voice as world number 182 Sweeny roared back from 5-3 down and took four straight games to claim the second set.

But even their cheers tapered as Monfils' movement diminished to a crab-walk across the baseline.

Sweeny rode an early break and took the third set, soon after Monfils' wife Elina Svitolina, the Ukrainian tennis professional, arrived at her husband's players' box for moral support.

A match seemingly headed for a deflating finish spontaneously re-ignited, though, as Monfils went for broke with his shots and the 24-year-old Australian froze with nerves.

Monfils thrashed a backhand down the line to break Sweeny and duly surged to a 4-1 lead.

The rally halted abruptly there, though, with Sweeny showing admirable composure to claim six of the first seven games and surge to his first win in a Grand Slam match.