Federer and Nadal returned from long lay-offs to take part in the first Grand Slam of the year in January 2017 as the duo were both underdogs in Melbourne.
However, both players rolled back the years, going through the competition and found themselves in the final again, bringing back nostalgia for tennis fans around the world.
In what was undeniably a classic with back-and-forth action, it was the Swiss ace who came out on top, beating Nadal 6-4, 3-6, 6-1, 3-6, 6-3 to lift his first Grand Slam since 2012.
Since then, the pair have continued their career resurgence, with Federer adding titles in Miami, Indian Wells, Halle and Wimbledon while the Spaniard also boasts five titles, including a 10th French Open title and his third US Open title.
McEnroe reflected on the duo's year so far, stating that he was surprised at how they dominated all the Grand Slams, starting from the classic in Melbourne.
"Of course I was surprised, I don't think even they thought they would win all four," McEnroe said, as quoted on Marca. "Their final at the Australian Open was the best game of the year. It has been incredible what they've done."
"If you don't play for six months, it is impossible to be at your best. Federer not only played well, but he showed great character. If you put everything together, it has been amazing."
Nadal is now world number one while Federer is the one player closest to the 31-year-old as he is currently ranked second, just under 2,000 points behind.
McEnroe believes Nadal is the favourite over Federer to end the year as world number one for the first time since 2013.
"I think Rafa is the favourite," McEnroe added. "Firstly, because of the advantage he has in terms of the points and secondly because I don't know how much Roger will play between now and November."
"Everything is possible, but Nadal has more chances to stay on top after the Masters."
As to whether Nadal can catch Federer's tally of 19 Grand Slam titles, being just three titles away, the American believes there is a chance.
"I don't know. In the beginning, I never would have thought they'd win two titles this year," he explained. "Of course Rafa can catch him if he is physically fit and respects his injures like he has this season."
"At Roland Garros, with the best of five sets, almost nobody can beat him and I think he'll win two more there for sure, but I think the same about Federer at Wimbledon. Both can continue to win."