"Keep playing Rafa, please, tennis needs you," Federer told the Spaniard during the trophy ceremony after winning a record-extending 18th men's major title at Melbourne Park that broke viewing records around the world and lit up social media.
As a former president of the ATP Players' Council, the 35-year-old Swiss superstar should know what he is talking about.
Sports thrives on strong rivalries, and in tennis nothing has come close to Federer taking on 14-time grand slam champion Nadal.
Since they first played each other on hard court in Miami in 2004, the former world No. 1s have contested 35 matches, including 22 finals. Between 2005 and 2015, there were only nine majors where one of them didn't feature in the championship match.
And since 2008, when their rivalry peaked in a Wimbledon final that is now widely seen as the best of all time, television ratings for men's tennis have grown 100% according to the ATP World Tour.
But with Federer turning 36 this year and Nadal 31, and both taking several months off last year to recover from injury, tennis fans may never see another clash between the sport's greatest and most popular male players.
"I hope to see you next year," Federer told the crowd at Rod Laver Arena. "If not, this was a wonderful run here and I can't be more happy to have won here tonight."
Although he later clarified his remarks and said he had no plans to retire just yet, tennis at the highest level is a grueling sport and it remains to be seen how well his body will hold up as the season progresses.
Which begs the question: Can tennis afford to lose the two biggest superstars the men's game has ever seen?
"My simple answer to that question is: No, they can't," said Alan Seymour, a sports marketing consultant and former professor at the UK's University of Northampton. "There will be a void in the short term."
Sports stars such as Federer and Nadal, plus Australian Open winner and now 23-time major singles winner Serena Williams and her sister Venus, "have taken on iconic status," Seymour said, adding it will be difficult to replace them once they retire.
In recent years, Seymour said, professional sports has often been tarnished by questions surrounding doping, match fixing and greed.
"Federer and Nadal have both stood against that in everything that they do," Seymour said. "They've been great ambassadors for the sport and they've given a lot back."
Chris Kermode, the ATP's chairman and chief executive officer, called Federer and Nadal "two of the most iconic stars to have ever played our sport."
TV ratings soar
The Australian Open men's final was a ratings winner for television companies, which pay major tournaments millions of dollars for the right to broadcast the event.
Australia's Channel 7 said the showdown between Federer and Nadal attracted 4.4 million viewers, its highest for an Australian Open men's final in 10 years. Eurosport said the match attracted a record audience of 16 million viewers across Europe.
Federer's successful return to tennis in Australia after six months off was also a winner for Grand Slam Tennis Tours, a Vermont-based tourism company specializing in high-end travel to the world's top tennis events.
Demand for travel packages to this year's Australian Open was 25% higher than last year, according to its president Andrew Chmura.
"Without a doubt, Federer drives the market more than any one tennis player ever has," Chmura said.
"When he plays, ticket prices move dramatically. When the schedule comes out and you see that Federer is playing at the night session instead of the day session, prices on the day session drop and prices on the night session increase."
Where is the next generation?
Although Kermode said the sport will miss Federer and Nadal when they go, he pointed to young players like Kei Nishikori, Grigor Dimitrov, Milos Raonic, Nick Kyrgios and Alexander Zverev as potential successors.
"The future of men's tennis looks promising, especially with such a strong group of emerging young players that come from such a geographically diverse spread around the world," Kermode said in an email.
Men's tennis may be experiencing an unprecedented golden era with the so-called "Big Four" of Federer, Nadal, second-ranked Novak Djokovic and top-ranked Andy Murray dominating most of the biggest events, but the generation that follows them has yet to make its mark.
Although Japan's Nishikori reached the 2014 US Open final and Canada's Raonic was a losing Wimbledon finalist last year, no man born in the 1990s has won a major.
At this year's Australian Open, rising German star and world No. 22 Alexander Zverev, the fifth-ranked Nishikori, Australia's world No. 15 Nick Kyrgios and world No. 8 Dominic Thiem of Austria all lost before the quarterfinals.
The exception was the 13th-ranked Bulgarian Grigor Dimitrov. Nicknamed "Baby Fed" because of the similarity of his game style to Federer, he lost a close five-set match to Nadal in the semifinals. The Spaniard had dispatched the big-serving Raonic the match before, while he was taken to five sets by 19-year-old Zverev in round three.
Power of sport
"We can't predict which players will break through on the biggest stages, yet we can have confidence in the capacity of our biggest tournaments to create stars in the future," Kermode said.
"Most sports are bigger than the best personality within that sport," he said. "In the end, people will come back to it. Ultimately the power of sport will always be a winner."