MELBOURNE, Australia -- Any Grand Slam tournament that features a championship match between the Williams sisters or Roger Federer and Rafael Nadal feels like hitting the lottery at this late date in their careers. But to enter Friday night with Nadal needing just one more throwback performance in Melbourne to assure both title showdowns would happen was beyond anyone's expectations when the Australian Open began.
The four of them have authored the two best rivalries of their generation, and there might be no need to confine the timeline to just that.
The bigger question is how do they keep doing this?
It's easier to make the argument that Federer-Nadal is, hands down, the best rivalry men's tennis has ever seen by any measure -- excellence and longevity, importance and drama. Right now, they have 31 Slam titles between them, more than the Jimmy Connors-Bjorn Borg-John McEnroe triad that raged against each other in the 1970s. They won a combined 26.
The argument about whether Federer is the best ever seemed settled for a bit since he owns a record 17 major titles despite not having won a Slam since 2012. But American Andy Roddick was spot on Tuesday at his Hall of Fame news conference when he pointed out Nadal's run here in Australia could reopen the argument.
Both the 35-year-old Federer and 30-year-old Nadal have looked good enough to revive the possibility that they could win more Slam finals somewhere else down the road -- perhaps as soon as at the next stop, the French Open, where Nadal has won nine times.
That could change everything.
"If you think about the historical significance," Roddick said, "[Nadal] at 14 Slams, [Federer] at 17 Slams, Rafa wins, it's 15-17. And it's back on. It's literally game on for the most Slams ever. If Roger wins, it's 18-14. I don't know that that divide gets made up."
That's why Roddick called the next Nadal or Federer major final "possibly the most important match in Grand Slam history." And he's right.
The question of how this is still possible for both men at this stage of their careers, or for Venus and Serena as they navigate their mid-30s, is a more ambiguous one to answer.
Men's tennis, even more than women's tennis, features some impressive depth at the top right now with established multiple Slam winners such as Stan Wawrinka, top-ranked Andy Murray and former world No. 1 Novak Djokovic still contending. A horde of younger players -- Milos Raonic, Dominic Thiem, David Goffin, Alexander Zverev and 25-year-old Grigor Dimitrov -- are trying to crash their way into the club.
Women's tennis is more in transition. Besides Serena, there isn't another player in the women's top 10 right now who's a surefire legend in the making.
Historically, the only women's tennis rivalry that eclipses the Williams sisters are the 88 lifetime matches -- including 60 finals -- between Chris Evert and Martina Navratilova that unfolded over 16 years. It left each woman with 18 major singles titles. For 12 consecutive years, from 1975 through 1986, either Evert or Navratilova ended the year ranked No. 1 in the world. They had a monopoly on the majors between 1982 and '86, too, winning 18 of the 20 Slams contested.
The Williams sisters rivalry has featured only 27 matches and eight major finals against each other heading into Saturday's meeting. Their encounters haven't always been as aesthetically pleasing as Navratilova-Evert's were, although both sisters said Thursday that the psychodrama of having to play each other has receded.
Where the Williamses have the edge is the eyeball test: They are dynamic players dominating in a more advanced era.
But both men's and women's tennis have trended toward those kinds of players during the Federer-Nadal/Serena-Venus years. So again, why are all four still formidable?
If you listen closely, the players themselves actually keep telling us their theories: It's not just that Serena and Venus, Federer and Nadal are extremely talented. The fact that they're still capable of winning these high-leverage matches also has something to do with their champion's pedigree itself and their ability to handle the pressure, doubt and challenges along with the physical grind. There's an intricacy and degree of difficulty to all of that, that we never see. And not every player solves it.
We saw that as underdogs CoCo Vandeweghe and Mirjana Lucic-Baroni wilted under the unaccustomed mental and physical duress of just getting to the semis of the Aussie Open.
We've seen it the past year as top-ranked Angelique Kerber and Garbine Muguruza confessed they've had to get acclimated to the pressure and expectations that come after winning even one Grand Slam.
We saw it again Thursday when three-time Slam champ Wawrinka -- as great a closer as there is in men's tennis right now -- double-faulted against Federer in the critical moment of the match. Federer was wobbling by that point, and he'd gone off court for treatment of an upper leg injury, but he steadied himself and finished of a five-set win he later admitted "I'm not sure I deserved."
Serena suggested something happens to certain tennis players when they've been in the crucible, and they find a way to succeed, not just survive. They unlock how to be consistently spectacular over time and deliver in the most important isolated moments, too.
Serena said Thursday that what happens during that forging process -- even the times she's failed before she succeeded -- has created "a better me."
Venus said what she's learned over the years is, "You can't stand still." You have to keep evolving to stay at the top and pair that with an unbreakable passion for the game even when results don't come.
Venus got a little lucky here when Vandeweghe's run took out Kerber and Muguruza before Williams had to face them. Nadal benefited from Djokovic being upset on his side of the draw. Federer got to avoid Murray, but he still had to beat No. 10 Tomas Berdych, No. 5 Kei Nishikori and Wawrinka in succession.
Like Federer, Serena hadn't played in five months before she arrived Down Under. She began her comeback with a bad loss in Auckland in a windswept second-round match pockmarked with 88 errors. Then she landed here and -- what do you know? -- resumed steamrollering everyone. Even more than the others, the intimidation factor she still throws off is an imposing thing.
Owning the past in tennis doesn't guarantee the marches through the draw that Serena and Venus, Federer and Nadal all enjoyed here. What the past wars have done is revealed who they are. All these years later, each player knows that even during the ultimate test of facing each other, whatever problems they're likely to encounter are things they've been able to solve before.
That's how they've kept becoming that "better" version of themselves that Serena mentioned and the sort of legendary players that others will remember long after the last balls they play bound out of reach.