Forget about aces or double-faults, winners or unforced errors: The statistic that has come to mean the most in tennis these days is "Grand Slam titles won." 

Which is why so much attention will be paid to Rafael Nadal, Novak Djokovic and Serena Williams at the Australian Open. 

Play begins at Melbourne Park on Monday (Sunday EST), with Williams and Djokovic among those on the schedule and Nadal's first-round match set for Day 2. Each match for each member of that trio is a possible step on the way to some history.

"People love records, don't they?" said Chris Evert, an 18-time major champion who now is an ESPN analyst. "I, for one, think that too much is made of Grand Slam wins."

This is Nadal's first chance to grab sole possession of the men's mark for most Grand Slam singles titles. He pulled even with Roger Federer at 20 by winning the French Open in October, beating Djokovic in a lopsided final. ( Federer is still sidelined after two knee operations).

Nadal has had stiffness in his back over the last two weeks, which kept him out of the ATP Cup and hampered his practice.

"The muscle is still tight, so is difficult to play with freedom of movements," he told a pre-tournament news conference Sunday. "Let's hope (the) situation keeps improving."

A second Australian Open trophy also would allow Nadal to become the first man in the Open era to win each Grand Slam tournament at least twice. He has 13 championships at Roland Garros, four at the U.S. Open, two at Wimbledon.

He still would have work to do to catch Williams: She already has 23 Slam singles titles (plus 14 in doubles and two in mixed doubles), the most by anyone in the Open era. Only one player owns more: Margaret Court, with 24 — 11 after professionals were admitted to major tournaments.

"It's definitely on my shoulders and on my mind," Williams said about 24. "I think it's good to be on my mind. I think it's a different burden, I should say, on my shoulders, because I'm used to it now."

And even if Williams' tour of a room where some of her hardware is displayed lit up social media, she made a point of explaining she finds other ways to define her value.

"My life is way more than a trophy. There's way more to me than a championship," said Williams, who turns 40 in September and last won a major title at the 2017 Australian Open while pregnant. "For me, every time I step on the court, I know I'm this tennis player, but at the same time I'm a mom, I'm a human."

She lost in the third round in Australia a year ago, then was hampered by an Achilles issue during a semifinal loss at the U.S. Open. That same problem forced her to withdraw from the French Open before the second round.

For Djokovic, in addition to trying to break his own record for most men's titles at the Australian Open by getting No. 9, and trying to ensure he will eclipse Federer for most weeks at No. 1 in the ATP rankings, there is the matter of closing the Grand Slam gap. 

Adding another major championship would give him 18 — two behind Federer and Nadal.

Other things to know about the 2021 Australian Open:

COVID-19

There aren't plans to regularly test players; 30,000 spectators will be allowed on the grounds per day, 50% of usual capacity but 30,000 more than at last year's U.S. Open. Still, the coronavirus pandemic will surely be a constant talking point the next two weeks. "I got a lot of messages from people in Europe saying, 'What's going on? Why are you not wearing a mask?' They were, like, 'What's happening?'" said 2020 runner-up Garbiñe Muguruza, a Spaniard. "And I was explaining that here, fortunately, they did well, and there is no cases, and that's why people are having a normal life." One issue that could be key: The lack of normal pre-tournament practice and preparation could lead to lackluster play or injuries.

ELECTRONIC CALLS

For the first time at a major tennis tournament, every match will be played without line judges present. Instead, calls will be made electronically. Most matches at the U.S. Open were done this way, but the two biggest courts retained the human element — and Djokovic was disqualified after smacking a ball that inadvertently struck a lineswoman in the throat.

RECENT CHAMPS

Sofia Kenin, a 22-year-old American, will be defending her first Grand Slam title. Iga Swiatek, a 19-year-old from Poland, will be playing in a Grand Slam tournament for the first time since winning a major championship — she beat Kenin in last year's French Open final. Swiatek acknowledged feeling "more pressure than usual," adding: "I know that it's hard, sometimes, to be back on tour after a win like that."

YOUNG MEN

Dominic Thiem ended a run of 13 consecutive Slam triumphs for Djokovic, Nadal and Federer by winning the U.S. Open in September, so now the question in men's tennis is: Who's next? Thiem, the 2020 runner-up to Djokovic in Australia, calls the 33-year-old Serb the favorite, but if some other first-time major champion is going to emerge, who might it be? Daniil Medvedev, Andrey Rublev, Stefanos Tsitsipas and Alexander Zverev are members of the group that has a shot.