Five thoughts: Federer-Nadal XIX

Swiss precision: Roger Federer has won eight of his 13 Grand Slam titles on hard courts. David Callow/SI

Rafael Nadal and Roger Federer have battled for tennis supremacy on the clay and grass courts of the French Open and Wimbledon for three years. On Sunday, their rivalry will break new ground when they meet on a hard court for the Australian Open title.

1. This is why we like rivalries

If Roger Federer wins? He ties Pete Sampras with his 14th career Grand Slam singles title, one more point in favor of his candidacy for the Greatest of All Time (GOAT). He will have beat Rafael Nadal in their first meeting at a major championship played on a hard court. He'll exact some revenge on Nadal after losing that epic Wimbledon final. After being dismissed last summer, Federer will have won the subsequent two majors and reclaim hegemony.

If Nadal wins? He will have claimed his sixth major title and first on a hard court -- at age 22. He'll improve his record against Federer to 13-6, including wins in the last five encounters. He'll solidify his hold on the No. 1 ranking. Suddenly, he's right in there for the GOAT discussion. No matter the outcome, it's a great narrative.

2. This match will reveal a lot

With a few obvious exceptions, Federer and Nadal almost seem to have made an unspoken gentleman's agreement: Nadal wins on clay and Federer wins on faster surfaces. Yet, for the first time in a Grand Slam, they'll be meeting halfway and playing on a court made of rubber but playing fairly slowly -- a "democratic surface" if you will. This could be a true test of supremacy.

3. Nadal's powers of recovery

After a lackluster start, Federer has looked as good as ever in Week 2 at Melbourne Park. He surrendered only three games to Juan Martin del Potro -- a top 10 player -- and then blew away Andy Roddick. He's been laying low since Thursday night. By contrast, even in the best of times, Nadal plays a violent, physically demanding game. Then consider that he is coming off a five-hour semifinal classic against Fernando Verdasco that didn't end until the wee hours of Saturday morning. It's entirely possible he'll have little in the proverbial tank and come out flat (in which case Federer owes Verdasco a case of wine). But apart from his youth, Nadal tends to rejuvenate quickly and his personal trainer, Rafael Maymo, specializes in recovery treatments.

4. Don't forget the Williams sisters

I'm writing this before the women's final. But in the event that Serena wins, it will mark still another triumph for tennis' first family. This will make three straight majors, plus the WTA year-end championship. Also, Venus and Serena won their third Australian Open doubles title Friday, the same day Serena passed Annika Sorenstam to become the highest-earning female athlete in sports history. I still maintain that this is the most remarkable story in sports, no matter how many times it's been told. Federer-Nadal will be the "takeaway" of this event; but let's not lose sight of the Williams sisters' sustained excellence.

5. Back to the men's final: where is Federer's head?

Among the lefty look, the superior defense, and unparalleled fighting instincts, Nadal has a unique mental effect on opponents, Federer included. For all his success of late, it bears mention that Federer has gone more than a year since solving Rafa. As John McEnroe recently noted, Nadal just "gets to" Federer the way no other player does. No bold prediction, but this match might well hinge on Federer's mental powers and his ability to handle Nadal's maddening game. The bar is set awfully high after last summer's Wimbledon showdown, but this should be another exceptional match. On the same day that Pittsburgh plays Arizona, here's hoping tennis gets its own Super Bowl.