Will Federer and Nadal meet again?

You may not notice it, but you are already a few seconds older now than you were a moment ago. And as you continue reading, even more irreplaceable seconds are flying by.

This isn't some crunchy granola observation about life. This is just basic physics, my friend. Time keeps on ticking, whether we're paying attention or not. There are some opportunities we'll get to experience over and over again, and some that will never happen again.

We should all keep that in mind as Roger Federer and Rafael Nadal continue their march to what would be an eighth clash in a Grand Slam final. Pay attention because, well, this opportunity may never come again.

Few so-called constants come to a sudden and dramatic ending the way they do in sports. And it seems no matter how many times we've seen the athletes we take for granted get drop-kicked in the mouth by Father Time, we can't help but continue to take their fleeting moments of brilliance for granted.

Mariano Rivera blow a save? Never.

Mike Tyson knocked out? Are you kidding?

The Patriots lose the Super Bowl? Come on, they haven't lost all season.

It used to be a foregone conclusion that Federer and Nadal would duke it out for at least one Slam per year. So we weren't paying attention when six Slams passed without them meeting. In fact, if one of them gets tripped up before Sunday, it would be the first time since 2004 we will go an entire year without the two facing off in a Slam.

And with Federer at 29 and playing less, Nadal's health an ongoing topic of conversation and, of course, the competition, there are certainly no guarantees they'll play each other in a final of any tournament in 2011.

That's not hyperbole, that's measurable fact: three years ago they faced each other five times for a title. The following year, four. Last year, it was only twice. And so far this year, they've played just once, in Madrid. How many of us saw or even remember that match? We took their battles for granted and while we weren't looking they have all but disappeared.

No one knew it was the beginning of something special when the two first played each other in the round of 32 at the 2004 Sony Ericsson. But that's how life is, you know? Some moments you can see coming, but usually, they just sort of happen.

If the two do meet up in Flushing Meadows this weekend, ESPN analyst Brad Gilbert said it would be the most important tennis match of all time. The 24-year-old Nadal is not only going for the career Slam -- something Federer didn't accomplish until he was 27 -- but he is also looking to be the first man in 41 years to win three consecutive Slams.

On the flipside, Federer is hoping to do more than just add to his collection of 16 majors. Despite all of his accomplishments, he still needs to silence the critics. After all, it's tough to be considered the best of all time if you're not even the best in your generation.

Sure Federer's overall resume is more impressive than Nadal's. But he is 7-14 against the Spaniard and hasn't beaten Nadal in a Slam in more than three years. And while the 2008 Wimbledon final is widely considered to be the greatest match ever played, I'm quite sure Federer would have preferred to be on the winning side of the worst match ever played.

That's why, while he may never say it, Federer knows he needs this title, this win much more than Nadal. If it is the last time they meet in a Slam final, then it is also Federer's last chance to avenge that heart-breaking loss at Wimbledon; wipe away the tears that uncontrollably fell when Rafa beat him in that epic match at the 2009 Australian; and even soothe some of the sting that came from each time he arrived at the French the No.1 seed but left as the second-best player.

Is it the most important match ever? I don't know. I still tend to go with Billie Jean King versus Bobby Riggs. But damn, this would be a very close second. Not only could it produce the most tension-filled tennis of the year, but all-time tennis supremacy is at stake. This match, if it happens, could place an asterisk on one player's career and an exclamation point on the other. But more importantly, it could be the period to what has become one of the greatest rivalries in all of sports.

In other words, a moment you don't want to miss.

LZ Granderson is a senior writer for ESPN The Magazine and a regular contributor to ESPN.com. He can be reached at lzgranderson@yahoo.com.