MELBOURNE (AFP) -- Two-time finalist Daniil Medvedev and US Open champion Coco Gauff swept into the second round of the Australian Open on Monday, Jan. 15, but Wimbledon winner Marketa Vondrousova was sent packing.

On a baking-hot day at Melbourne Park, men's seventh seed Stefanos Tsitsipas and 16th seed Ben Shelton also tasted victory, ahead of Naomi Osaka's Grand Slam comeback on Rod Laver Arena in the evening session.

Third seed Medvedev battled tough conditions on Margaret Court Arena against French qualifier Terence Atmane, who smashed his racquet, served underarm and retired in tears after suffering bad cramping that forced him off court while losing 5-7, 6-2, 6-4, 1-0.

"When I started to feel tough physically he started cramping, so it was brutal conditions," said Russia's Medvedev, a finalist in 2021 and 2022.

"I was getting tired but many times in these situations the other guy is getting tired too and it's about who manages it better."

The Russian will face Finland's unseeded Emil Ruusuvuori in the next round.

Tsitsipas, who lost last year's final to Novak Djokovic, was stunned by Belgian lucky loser Zizou Bergs in the first set, but woke up to take complete control and win 5-7, 6-1, 6-1, 6-3.

The Greek star was due to meet Italian Matteo Berrettini, but the former world number six withdrew with a foot injury on Sunday.

Women's fourth seed Gauff said ahead of the opening Grand Slam of the year that she wanted to win "multiple" major titles after her breakthrough at Flushing Meadows in 2023.

The 19-year-old put the plan into motion with a 6-3, 6-0 rout of Slovakia's 68th-ranked Anna Karolina Schmiedlova on center court.

'Didn't play good'

"I was a little bit nervous coming in today. Probably could tell. I was able to just calm down and then play my good, not my best, but good tennis," said Gauff, who successfully defended her Auckland title in the lead-up.

Her reward is a clash with unseeded American Caroline Dolehide in round two.

While she lived to fight another day, it was curtains for Vondrousova, who slumped 6-1, 6-2 to Ukrainian qualifier Dayana Yastremska.

The Czech seventh seed pulled out of the warm-up Adelaide International last week with a hip injury and said she was also struggling with a sore shoulder, which affected her serve.

"I didn't practice much before the tournament because I was injured," she said after becoming the highest seed to depart so far.

"She played a good match, I didn't play good, that's why (I lost)."

World number 93 Yastremska, whose best showing at Melbourne Park is a third-round appearance in 2019, sported the slogan "Be brave like Ukraine" on her bag and said she wanted to keep the war in her homeland in the spotlight.

"I'm very proud of Ukraine, proud of the people, proud of the warriors and the civilians," she said, after setting up a clash with unseeded Frenchwoman Varvara Gracheva.

Another Ukrainian, Elina Svitolina, also progressed, demolishing Australian Taylah Preston for the loss of just four games.

New mum Osaka, 26, is the main attraction in the evening session, having stepped away from the sport in September 2022, citing mental health concerns.

After giving birth to a baby girl, Shai, in July, the Japanese star decided to return for the 2024 season.

But she faces a huge challenge first up against 16th-seeded Frenchwoman Caroline Garcia.

"I have a much more positive mindset and a much more grateful mindset," four-time Grand Slam champion Osaka said of returning to Melbourne, the scene of her title-winning exploits in 2019 and 2021.

They will follow on from local hope and 10th seed Alex de Minaur's showdown with big-serving Canadian veteran Milos Raonic

Other players in action include five-time Australian Open finalist Andy Murray and women's sixth seed Ons Jabeur.