The performance Roger Federer and Rafael Nadal teamed to produce at the Australian Open has left both men with a problem.

It's a good problem to have, but it's still a problem.

Fans, being fans, expect the world of them now that Federer has won his 18th major, adding to his all-time record, and Nadal has rediscovered his confidence, not to mention the bite in his forehand. But given the realities governing each man's career, just how much should each expect of himself? How hard should he push?

Those are intriguing questions that pose tough choices and might have career-influencing ramifications. When Federer was asked by a reporter after the final if he was gratified to win major No. 18 -- thus putting more distance between himself and his main rivals (Nadal being chief among them) -- he replied: "That's [not] what I see. The last problem is the slam count. Honestly, it doesn't matter."

Nadal, having lost, was in a slightly different position. But his view of the future also firmly shut out visions of major titles hanging like fruit to be plucked. He told the media after the final that he thinks he can win titles if he keeps playing the way he did in Melbourne, but "more than all these kind of things is being healthy enough to work the way I need to work, to fight for the things I want to fight for."

The sentiments of both men are understandable. Unlike the fearless 25-year-old warriors they once were, they can't get greedy for those Grand Slam titles. On the other hand, both have spent their adult lives pursuing the majors; neither will be doing cartwheels if he makes the second week at the next major or loses in a Masters 1000 quarterfinal.

Ineludible considerations shape the attitudes of both men. Federer is 35 years old; Nadal, while five years younger, is chronically injured. Despite their heroic resurgence, neither man is in the top four in the rankings: Nadal is No. 6, and Federer just made it to No. 10 by winning Down Under. That means they could face each other -- or one of the top four, or anyone else ranked above them -- before the semifinals at any tournament.

If the two titans had won two or three rounds apiece in Melbourne and gone quietly into the night, there would be less urgency for them to secure higher rankings with the heart of the tennis year coming up.

Meanwhile, both must navigate a number of unknowns.

In winning the Australian Open, Federer dutifully ticked off one of the very few still empty boxes on his application for GOAT status. He produced a mind-blowing, unexpected triumph when most people had written off his chances.

The last player to do that was Pete Sampras, who endured a sometimes miserable 26 months before he caught fire and won the US Open in 2002. Sampras never picked up a racket again, except to fool around. Federer's drought was even longer: His last major win was at Wimbledon in 2012.

Federer and Sampras, while friends, are very different men. Sampras agonized and suffered through the final stages of his career. Federer appears to have enjoyed every moment of his and shows no sign of the late-career jadedness that afflicted Sampras. If anything, he loves the game more than ever and luxuriates in his status.

Rafael Nadal gives Australian Open champion Roger Federer a pat on the shoulder after the longtime rivals met in a Grand Slam final for the ninth time. Martin Richard/Presse Sports via USA TODAY NETWORK

But then, Federer is still winning. Always has been. (In his last match before the Australian Open, he was a Wimbledon semifinalist.) At some point he won't be, even though he's Roger Federer. Nobody knows when. And nobody really knows how this magnificent achievement will impact Federer.

"I think this one will take more time to sink in. When I go back to Switzerland, I'll think, 'Wow.'" Federer said. "The magnitude of this match is going to feel different. I can't compare this one to any other one except for maybe the French Open in '09."

There's a difference, though. Federer was at the midpoint of his career in Paris in '09. Now he's closer to the end. That's where grinding out those second- and third-round matches can become tedious. That's where all athletes are forced to hear that irritating, inescapable voice whispering, "It's best to go out on top, while you're still a winner."

There's also this: Federer took medical timeouts at critical moments late in his semifinal against Stan Wawrinka and also in the final. Some suspected him of gamesmanship, but neither of his opponents backed the charge.

The detail lost in the debate over the ethics is that Federer felt he needed to exploit the medical timeout rule for the first time in his career. This was a man in his first tournament after a six-month hiatus. It was a reminder that he's 35.

Nadal must wish that he might have Federer's physical problems -- and no more -- when he turns 35. As he kept telling people in Australia, he's just happy to be healthy again. Nadal's great source of concern -- and it tints almost everything he says, like a garment that ran in the wash -- is that his body has taken to betraying him on a regular basis, in different ways.

Take last year. Still haunted by a lack of confidence, Nadal was upset by volatile Fernando Verdasco in the first round of the Australian Open. He took significant strides rebuilding his game through the spring, but a wrist injury suffered in Madrid forced him to pull out of the French Open before his third-round match.

On the evidence we saw in Australia, Nadal could reclaim his "King of Clay" title this spring. But he will have to remain healthy, and he will have to deal successfully with the same kind of pressure that caused him to implode in 2015. Remember, Nadal reached the quarterfinals before losing to Milos Raonic in the quarterfinals at Brisbane before the first major of the year. He's off to a great start, but it's just start.

Federer and Nadal are largely exempt from the commitment demands of the ATP World Tour. But they must play if they want to continue making headway in the rankings. Right now, both are entered in one warm-up event followed by the two upcoming U.S. hard court Masters 1000s.

The great rivals savored their accomplishment in Australia. They weren't looking ahead. Some observers actually detected a coded, final farewell to the Australian Open when Federer told the Melbourne crowd he looked forward to seeing them "if" he returned in 2018.

Later, Federer explained, "This is all about, you know, knowing that I have only so much tennis left in me. If I do get injured, maybe if I miss next year. Who knows what happens? You never know if you're going to have an opportunity at this stage [again]."

That was a sentiment Nadal, who hasn't made a victory speech at a major final since the spring of 2014, understood all too well. But he and Federer showed there might be plenty of tennis left in them yet. We'll see how they ration it out.