Bill Tilden did not lose a single tennis match of substance for seven years, between 1920 and 1926. He was so dominant a player in his time that he would often purposely lose points and games and even sets just to make the matches a little bit more interesting. One of his favorite tricks, when he seemed in trouble, was to hold five tennis balls in one hand, serve four consecutive aces, and throw the fifth ball away disdainfully.

Don Budge was an American amateur tennis player who in 1937 and 1938 played in six consecutive grand slam tournaments -- he won all six. He also led the U.S. to their first Davis Cup championship in more than a decade. He turned professional and, shortly after that, went to war.

Pancho Gonzalez was the No. 1 ranked player in the world for eight consecutive years, an unmatched record, and numerous experts including Bud Collins have said that if you needed someone to play a tennis match for your soul, you would choose the temperamental and brilliant Pancho Gonzalez. Rod Laver won tennis’ Grand Slam in 1962 then turned professional, which prevented him from playing at any of the four -- the Australian Championship, the French Championship, Wimbledon or the U.S. Championship -- for five years. Then in 1968, those tournaments opened up to professionals (which is why we call them “Opens” now). One year later, Laver won the Grand Slam again.

Bjorn Borg won the French Open and Wimbledon -- widely viewed as the two most prestigious and the two most different tennis tournaments -- back-to-back in 1978, 1979 and 1980. No man or woman has ever even pulled that double two years in a row, much less three, Borg retired when he was 26 years old and had grown bored by tennis.

Pete Sampras won Wimbledon seven out of eight years and is widely believed to have the greatest serve -- that uncommon combination or power, accuracy and consistency -- in modern tennis history.

Andre Agassi was the first male tennis player to win the career grand slam -- winning in the heat of Australia, on the red clay of Roland Garros, on the lightning fast grass at Wimbledon, and in the New York mayhem of the U.S. Open -- since Roy Emerson 25 years earlier.

Still, most of us seem pretty sure that the greatest tennis player of all time is either Roger Federer or Rafael Nadal who happen to be playing now. There seem to be a couple of major reasons for this.

One: Federer and Nadal are piling up grand slam championships in unprecedented numbers. Federer has won 17 of them, which is the record, and he reached the final of another seven. From Wimbledon 2005 until the Australian Open in 2010 he reached the final of all but one grand slam championship. Nadal, meanwhile, has a chance to win his 14th grand slam in Australia this weekend, that would tie him with Sampras for second place on the list.

Two: Federer and Nadal play in a time where the equipment -- specifically the tennis rackets but it’s everything including shoes, training and so on -- offer more power, precision and consistency than at any time in the history of the sport. Federer and Nadal (along with Novak Djokovic and Andy Murray) are visibly playing better tennis than all of their predecessors, including players of just a few years ago. If you match up the high-def video of Federer against the grainy color of John McEnroe or the black-and-white crackle of Ken Rosewall ... it’s almost ridiculous. It’s obvious these guys today are hitting the ball much harder with much more spin and at angles that were simply unattainable with older tennis rackets.

But are these good reasons to declare today’s players the Greatest Of All Time? The grand slam numbers are clearly not a good reason. Federer and Nadal (and Sampras before them) happen to play in a time when the world is a lot smaller and the top tennis players go to every grand slam event all over the world. This wasn’t even close to true before. Rod Laver won 11 grand slam events but he missed TWENTY major tennis events in his prime because he had turned professional. When you consider he won the yearly Grand Slam on both sides of that, it seems all but certain that he would have won more than six of the 20 majors he missed (he won eight professional majors during that stretch). Laver, certainly, would have the record.

Borg only played in Australia one time and that was before he won his first Wimbledon. Jimmy Connors won the Australian Open the first time he played it in 1974, reached the final the next year, and never played there again -- he also skipped five consecutive French Opens during his prime. John McEnroe routinely skipped the Australian and French Opens also. Bill Tilden entered only eight events we now consider grand slam titles in his prime. He won all eight.

This is not to downplay the amazing performances of Federer and Nadal. Heck, Federer set the record by reaching an almost unbelievable ten consecutive Grand Slam finals, and after that had another stretch where he reached eight consecutive finals. Nadal has lost one match -- ONE MATCH -- at Roland Garros and has beaten Federer nine of the 11 times they have faced at a major tennis championship. But to say that either one was better than Laver or Borg because they have more grand slam victories is silly.

The modern equipment question, though, is the one that really muddles the GOAT conversation. There is absolutely no question in my mind that Nadal or Federer, with current training and modern tennis rackets, would utterly destroy Bill Tilden or Rod Laver or Bjorn Borg using the equipment of their time. It would be like a first-round match against a qualifier. Pat Cash, the Wimbledon champion in 1987, has said that he could beat HIS YOUNGER SELF (he’s now almost 50) if he was using today’s equipment. One tennis pro told me that the difference between today’s rackets and rackets from just ten years ago is light years, forget about going back 25 years to the time of wood and steel. Tennis with today’s equipment is simply a different game than it was.

The same is true for golf, by the way, though probably not quite to the same extreme. Tennis technology is advancing so fast that the game probably resets every 10 or 15 years. The tennis players today ARE playing the game better than at any time in the history of the sport. And the previous generation was playing the game better than it had ever been played before that. And so on. That doesn’t mean the greatest players in the history of the sport are on the court now. Jimmie Johnson drives his car a lot faster than Richard Petty did. That doesn’t mean -- and Johnson himself would never suggest -- that he’s a better driver than Petty was. Times change.

The one thing that seems clear is that Rafael Nadal is better than Roger Federer. Rafa is five years younger and so the timing is a little bit off. Nadal was not quite ready to compete with Federer on anything but clay from 2004 to 2007 or so. In those four years, Federer won 11 grand slam championships:

2004 Australian over Marat Safin 2004 Wimbledon over Andy Roddick 2004 U.S. Open over Lleyton Hewitt 2005 Wimbledon over Andy Roddick 2005 U.S. Open over Andre Agassi 2006 Australian over Marcos Baghdatis 2006 Wimbledon over Nadal 2006 U.S. Open over Andy Roddick 2007 Australian over Fernando Gonzalez 2007 Wimbledon over Nadal 2007 U.S. Open over Novak Djokovic

It was a remarkable run. Nadal dominated him on clay, beating him three times at the French Open. But no one else could touch Federer on any other surface. And then, Nadal ascended. He utterly destroyed Federer at the 2008 French Open (losing just four games) and has not lost to Federer in a major tournament since. Nadal beat Federer on what had been his home court of Wimbledon in 2008. Nadal beat Federer at the Australian Open in 2009 -- that was the loss that broke Federer and left him in tears. And since then, at grand slams, Federer has not even been able to push Nadal to five sets, much less beat him. They have played 33 times in total, and Nadal has won 23 of them. And Nadal has beaten Federer nine times in majors; Federer has only beaten Nadal those two times at Wimbledon before Nadal had figured things out.

I’m a Federer fan as is a good friend of mine, and we often try to come up with reasons to keep Federer above Nadal on the all-time list. We keep coming back to the age difference (Nadal didn’t really play Federer much in his prime), though we also both know that Federer’s prime stopped abruptly when Nadal came of age. We keep coming back to Fed’s edge in total grand slams, but we both know that’s pretty weak. We both know that Nadal will probably pass Federer on that list too.

Plus, if Nadal wins the Australian Open, he will become the first man in the Open Era to win the double career grand slam -- that is, win each grand slam event two times. Even Federer could not do that.

Before Federer and Nadal played at the Australian Open this week, we kind of had some hope that Federer would pull this one out. Fed had played brilliantly up to that point and Nadal was having some trouble with blisters and his second serve. The Australian Open is on hard courts which seem to be Nadal’s weakest surface (though this is like saying that LeBron James’ jump shot is the weakest part of his game -- true, but he’s still better than almost anyone else). We believed because we desperately wanted to believe that Federer had found his youth because he had changed rackets and had started working with the great Stefan Edberg and seemed so confident.

Nadal ran him off the court. Nadal has always been able to hit scorching and hopping topspin shots to Federer’s backhand and Federer -- remarkable as he is -- has never really able to handle that. Nadal did some of that but for good measure he also ripped backhand winner after backhand winner, leaving Federer looking all but helpless. It was a straight-set thumping, and Federer left with no illusions. He turns 32 this year and if he’s ever going to win another major championship, he will need someone to take out Nadal for him. Djokovic too, probably.

And watching Nadal play that kind of mind-blowing tennis, I thought what I’m sure many people think these days: Nadal is the best tennis player who ever lived. This might not be true. Give Laver these rackets and training, give Borg or McEnroe or Tilden these rackets, give Gonzalez or Sampras or Budge these rackets, and there’s no telling what would happen. But this much is certainly true: No one ever played tennis the way Rafa Nadal plays now.