MELBOURNE, Australia -- Australia prides itself on being progressive, ahead of the curve.

A government-funded universal healthcare system was introduced in 1984. Six years before Hillary Clinton ran against Donald Trump, Julia Gillard was the first woman to serve as prime minister.

And, although "Down Under" sounds a tad behind the times, Australia is actually 16 hours ahead of the Eastern time zone.

Likewise, the Australian Open has been a leader in its narrow sphere, building the first roof over a major court -- there are three now, one more than the other three Grand Slams combined.

This year, however, there's been a serious step back. The tournament is experiencing a back-to-the-future wave of nostalgia. Both No. 1-ranked players, after ascending the throne for the first time at the end of 2016, were dispatched by unusual sources and, suddenly, it's the aughts all over again.

Serena Williams, already the oldest women's Grand Slam champion ever, appears poised to run her major total to 23, which would send the 35-year-old careening past Steffi Graf, with whom she is tied for the Open era record.

After six months off thanks to an injured knee, 35-year-old Roger Federer looked as frisky as a baby kangaroo in knocking off a pair of top-10 players, Tomas Berdych and Kei Nishikori.

Rafael Nadal, now 30, hasn't won a Grand Slam in nearly three years, but a vintage victory over German teenager Alexander Zverev left some folks wondering if a10th title at Roland Garros might just be possible.

And venerable Venus Williams, the oldest woman in the draw, is into another major quarterfinal at the age of 36.

Yes, there's an unmistakably retro reverb in the air here at Melbourne Park, and it feels so good. Legends' doubles is a staple at the Grand Slams, but this is legends' singles.

It is becoming more and more likely that Serena and Venus could play in the Australian Open final -- 14 years after they met in the championship Down Under for the first time. Sean Garnsworthy/Getty Images

In the wake of Serena's straight-sets victory over Barbora Strycova on Monday, it was actually possible to imagine that wondrous time in 2002-03 when she produced a four-peat, the Serena Slam, and beat Venus in all four finals. Possible to conjure images of Nadal and Federer at Roland Garros in 2006, their first of eight major finals.

The crazy thing? On the eighth day of the tournament, more than a decade removed, both of those matchups were still potential finals here.

In 2002, Thomas Johansson, playing legends' doubles, was the men's winner here.

"Yeah it is [like 2002]," he said. "Now it's wide open. OK, you can say maybe this player might be the favorite to go deep, but it's wide open, anyone can win it. It would be amazing if it was another Federer-Nadal final."

Like khakis and a blue blazer, great champions never go out of style.

Martina Hingis, 36, and Leander Paes, 43, aren't seeded in mixed doubles, but they're already through to the quarterfinals.

Serena was asked if people should be impressed with her staying power.

"I think it's impressive," Serena said, not so modestly. "I think in general people our age aren't really playing at a top level, so indeed, it's definitely impressive.

"Venus and I are mentally 8 and 9, so that's why we're probably able to play a little better."

This was one of those days when Serena was not at her best. In the end, it didn't matter.

"I feel like everything depends on Serena," said a frustrated Strycova. "If she has a good day, you kind of don't have a chance, because she plays so well and she plays so quick and her game is so tough to get in the rhythm.

"So today, I felt like I am there but still far away."

That's how a lot of the younger players are feeling.

Jennifer Brady, the 21-year-old American qualifier, was beaten by 34-year-old Mirjana Lucic-Baroni, who incredibly went 19 years between winning matches at the Australian Open.

Stan Wawrinka and Jo-Wilfried Tsonga -- both 31 -- play in a Tuesday quarterfinal. The winner will play the winner of the Federer-Mischa Zverev match. It's typical of this fortnight that Zverev is 10 years older than his brother Alexander, who is seen as a possible future No. 1.

For the second straight year, Serena shut down her season after the US Open, raising questions about her motivation. Based on her results here, she wasn't just focusing on social media the past few months. Venus, who still deals with the effects of Sjogren's syndrome, an energy-draining condition, trained with her side by side in Palm Beach Gardens, where they share a home.

"She had a really intense preseason," Serena said. "I feel like when you put in the hard work, the results, eventually, they show up."

At this Australian Open, some of these singles' legends could show up in the final.