Change will be afoot, as well as underfoot. At the end of the match, we will be in the presence of arguably the Greatest Ever or unarguably the Greatest Right Now.
A win for Federer would tie him with Pete Sampras at 14 Grand Slam titles and, in the eyes of many, would lift him above the legendary American on the strength of three French Open finals and a more concentrated dominance during his peak.
A win for Nadal would give him a stranglehold on both the men's game and the rivalry against Federer. He would become the holder of three Grand Slams on three different surfaces, with wins over Federer in the finals of each.
This latest and perhaps most exciting clash of the titans was only secured at 1:07 a.m. on Saturday morning after a 5-hour, 14-minute battle between Nadal and fellow Spanish lefty Fernando Verdasco in the semifinals. It was the longest match in Australian Open history, eclipsing the 5-hour, 11-minute match between Boris Becker and Omar Camporese in 1991.
The tears were already welling up in Nadal's eyes as he reached triple match point in the fifth set, and after Verdasco hit a double fault on the third match point to send the world No. 1 into his first Australian Open final, the emotion spilled over and sent him flat on his back in delight. It's a celebration Nadal usually saves for winning the title.
"It was very emotional today. Well, it was amazing match, no?" Nadal said. "One of these matches you're going to remember long time."
Even Federer was watching in the early hours of the morning. "I went for dinner and saw the end. It was really exciting. It was an unbelievable match," he said.
The length and intensity of the prelude will add even more intrigue to Federer-Nadal XIX on Sunday night in Melbourne.
The vanquished Verdasco, who is good friends with Nadal, feels that playing the men's semifinals on consecutive days gives the winner of the first semifinal a significant advantage. Federer completed a fairly routine 6-2, 7-5, 7-5 win over Andy Roddick on Thursday evening.
"I think for sure the semifinals supposed to be the same day because I think is the most fair for everybody," Verdasco said. "Yesterday Federer play three sets. And today Rafa play five sets, five hours, and he will have one day less [to recover]."
Nadal described his situation as "unlucky," saying, "For sure Roger is going to be in much better performance physically than me for the final. But at the same time I'm going to try to be recovered for the final and play my best."
Federer isn't counting on a weakened Nadal, however. "I don't think Rafa will struggle too much to get over this kind of a match," said Federer, who battled back from two sets down in the fourth round and has cruised since. "He's had had an easy tournament so far. This was the tough one."
Aside from this unknown element, the balance looks tantalizingly even.
Their previous Grand Slam meetings have been evenly split between Nadal's turf (the red clay of the French Open) and Federer's turf (the green grass of Wimbledon). It was Nadal's epic five-set victory at Wimbledon last year that finally tipped the balance and set the stage for his ascension to No. 1.
Now, for the first time, the match will take place on neutral territory. Melbourne's Plexipave hard courts are fairly quick, but the balls tend to fluff up on the gritty surface, lending some advantage to both Federer's shot-making and Nadal's heavy topspin.
The beginning of Sunday's match will be closely watched to see if the height of Nadal's shots can still hamper Federer or whether the Swiss can add the little extra zing to keep the Spaniard in defensive mode.
On balance, the slight edge in surface probably goes to Federer. Nadal has yet to establish a record of consistent success on hard courts, despite some good results last summer that included winning the gold medal at the Olympics.
The edge in matchup, however, is unquestionably Nadal's. Almost five years younger than Federer, the 22-year-old Nadal has won 12 of their 18 meetings. He has also doubled Federer in their Grand Slam finals, going 4-2.
Federer does hold a 3-2 edge in their hard-court meetings, though the last came indoors in 2007 at the Masters Cup in Shanghai.
Both know what is at stake this time around, for them as individuals and the potential impact it could have on behalf of the sport.
"For me it's amazing to play another final of Grand Slam -- here in Australia, the first one," said Nadal, who has faced Federer in all but one of his eight major finals. "For sure, I prefer another opponent. But that's [what] makes big the sport, too, no? Finals like this."
"It's an unbelievable opportunity for me, of course, not being No. 1 anymore [and] trying to beat No. 1 in the world and get the 14th Grand Slam," Federer said. "This is where I won the Grand Slam to become No. 1 in the world back in 2004, so I've always had a special liaison with this tournament.
"The stage is set, basically, for a great match."
Only one can triumph Sunday, but "the rivalry" will be a winner either way.
Kamakshi Tandon is a freelance tennis writer for ESPN.com.