Melbourne, Jan 19 (AFP) Old stagers Novak Djokovic and Serena Williams will aim to keep the younger generation of players waiting in the wings as Grand Slam tennis enters a new decade at the Australian Open on Monday.

After recent bushfire smog largely cleared in Melbourne, the view is all too familiar with Djokovic and Williams, who is seeking a record-equalling 24th Major title, installed as the bookies' favourites.

Top seed Rafael Nadal, 33, is celebrating becoming world number one in a third decade while Roger Federer, 38, is trying to defy the ageing process and stay ahead of his rivals with a 21st Grand Slam win.

The start of 2020 is not dissimilar to 2010, when Federer and Nadal shared the four Grand Slam titles and Williams won in Melbourne and Wimbledon.

Ten years later, the men's Big Three -- who have won all but two Australian Open titles since 2004 -- occupy the top three rankings, and Williams is one step away from Margaret Court's record for Grand Slam victories.

The men's dominance is stark: since Federer won his first Grand Slam title in 2003, only five Major finals have not featured one of the Swiss, Nadal or Djokovic.

Several challengers have come and gone but there is increasing hope for the men's up-and-comers, while nine women have won Grand Slam titles since Williams, 38, claimed her 23rd in Melbourne in 2017.

- 'They're very close' -

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While Djokovic and Nadal split last year's Grand Slams, Dominic Thiem, Daniil Medvedev and Fabio Fognini won their first Masters trophies and Stefanos Tsitsipas, 21, became the youngest ATP Finals champion in 18 years.

"They're very close. I don't think that's miles, miles away maybe as it was some years ago," Djokovic of the NextGen winning a Major title.

"I think they are definitely hungry. They're challenging. They're knocking on the door."

The clash between old and new will be epitomised in the first round on Monday, when Venus Williams, who turns 40 this year, plays 15-year-old rising star Coco Gauff -- who wasn't even born when her fellow American lifted her first Grand Slam trophies in 2000.

Japan's Naomi Osaka, 22, is defending a title for the second Grand Slam in a row after her repeat bid at last year's US Open fell flat in the fourth round.

World number one Ashleigh Barty, fresh from winning the Adelaide International on Saturday, carries Australian hopes of seeing the first home-grown women's winner since 1978.

"Obviously it's the perfect preparation. But regardless of whether I won the title or not last week, I feel like I'm well-prepared," Barty said.

"I'm happy, I'm healthy. I'm coming into the first Grand Slam of the year with a smile on my face. That's all I can ask of myself."

The tournament is taking place against the backdrop of a bushfires emergency that has swept the nation and ramped up fears over global warming -- and billowed choking smog across Melbourne and other cities.

After player anger during qualifying and practice, when several were hit by coughing fits and breathing problems, air pollution returned to 'moderate' levels over the weekend, with rain forecast for the start of the tournament. (AFP)

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