Rafael Nadal plays a forehand in his match against Laslo Djere of Serbia during the Australian Open at Melbourne Park on Tuesday in Melbourne, Australia. Photo: VCG

Rafael Nadal eased concerns over his injured back as he made a fast start to his bid for a record 21st Grand Slam at the Australian Open on Tuesday.

On a day when women's champion Sofia Kenin also went through, but two-time winner Victoria Azarenka lost after breathing problems, Nadal appeared untroubled in his first match of the year.

The Spanish great, who pulled out of last year's ATP Cup with back problems, beat Serbia's Laslo Djere 6-3, 6-4, 6-1 in one hour and 52 minutes on a sun-kissed Rod Laver Arena.

"It's been a tough 15 days for me… My back is not perfect," said the 2009 champion, whose only appearance this year had been an exhibition against Dominic Thiem in Adelaide 12 days ago, where he first experienced stiffness in his back.

"There is always a chance to improve, and that's why I'm here playing and fighting to try to get better and then give myself a chance."

The injury forced him to make changes in his service action against Djere, who didn't have the weapons to trouble the second seed despite Nadal being below par.

"Today it's not great. I needed to change a little bit the motion of my serve," he said. 

"I need to go day-to-day and just try to stay positive. I'm trying to do all the things possible to be ready for compete."

Nadal, 34, is bidding to outstrip his old rival Roger Federer, who is missing the tournament as he recovers from surgery, and take sole ownership of the all-time record for Grand Slam titles.

After world No.1 Novak Djokovic eased through late on Monday, Russia's Daniil Medvedev extended his winning streak to 15 matches with an emphatic 6-2, 6-2, 6-4 victory over Canada's Vasek Pospisil.

The 2019 US Open finalist is raising hopes of a maiden Grand Slam title with his unbeaten run, which includes winning the Paris Masters, ATP Finals and last week's ATP Cup with Russia.

"I didn't know how it would be physically, but I managed to finish it fast and I'm feeling good," said the world No.4. "I had to go out and win the match because that's my job."

Russia's seventh seed Andrey Rublev also continued his unbeaten start to the year with a straight-sets win over German Yannick Hanfmann 6-3, 6-3, 6-4.

'Not happy' 

Women's champion Kenin was less convincing and she audibly vented her frustrations during her 7-5, 6-4 against Australian Maddison Inglis, who is ranked outside the top 100.

"I'm obviously not happy with the way I played," said Kenin, 22, who made 27 unforced errors on her return to Rod Laver Arena. 

Two-time major winner Garbine Muguruza, who was stunned by Kenin in last year's final, had little trouble beating Russia's Margarita Gasparyan 6-4, 6-0.

But there were distressing scenes as an ailing Azarenka, the 2012 and 2013 champion, went out to Jessica Pegula on the second day of the coronavirus-­delayed Grand Slam.

Azarenka, who was one of the players locked down in hard quarantine before the tournament and not allowed out of her room to train for 14 days, began to suffer in the second set.

The 2020 US Open runner-up, who only played one warm-up match last week, was seen gasping and using an inhaler, and then looked close to collapse on court. After a medical timeout she played on but lost 7-5, 6-4.

Elsewhere fifth seed Elina Svitolina of the Ukraine was pushed hard by Czech Marie Bouzkouva before coming through 6-3, 7-5 (7/5).

And 16-year-old American Coco Gauff, who beat Venus Williams and Naomi Osaka en route to last year's round of 16, had a straightforward 6-3, 6-2 win over Switzerland's Jil Teichmann.

Women's world No.1 Ash Barty was to open the night session on Rod Laver Arena as she aims to become the first Australian women's champion since Chris O'Neil in 1978.

Barty, fresh from winning the Yarra Valley Classic final against Muguruza on Sunday, plays Montenegro's Danka Kovinic.

The year's first Grand Slam has started three weeks late because of coronavirus problems, with players and officials required to quarantine for two months after arriving in Australia.

Crowds are limited, masks are mandatory and movement is curbed around Melbourne Park, where Monday's attendance was 17,922, compared with 64,387 on day one in 2020.