The legendary pair rolled back the years to dominate the men's tour, each winning two grand slam titles and finishing the season as the top two players in the world.
Federer won the Australian Open and Wimbledon to take his major tally to 19, while Nadal claimed a 10<sup>th French Open and the US Open on his way to finishing as the year-end world number one.
Their success came amid season-ending injuries to Andy Murray and Novak Djokovic and the emergence of Alexander Zverev and improvement of Grigor Dimitrov and Nick Krygios.
While Nadal withdrew from a string of events during the back-end of the season in an effort to manage an ongoing knee problem, Federer missed the entire clay court swing to ensure he was fit for the second half of the campaign.
And according to Annacone – who coached Federer for three years and also worked with Pete Sampras – the way both players conditioned themselves was key to their success.
"To lose Novak [Djokovic], Stan [Wawrinka], Andy [Murray], [Milos] Raonic and [Kei] Nishikori, that is a lot," he told Sports Illustrated. "It is interesting that the two guys who managed top have the best years were the old guard. A lot of that is because they know how to manager their bodies so well.
"For Rafa the year's rigours are starting to show up in the knees. He played a lot of tennis this year. Roger obviously played less but knew how to manage his schedule so well.
"The first part is the participation the fact that Nadal and Federer were the stalwarts and the second part is at their age they dominated. It is unbelievable to think they split all four majors and they both had ridiculously good years, so I find that exciting.
"You wonder if Federer and Nadal are ever going to get old, or bored."
The dominance of Federer and Nadal will be challenged in 2018 when the likes of Murray and Djokovic return to full fitness.
Both Djokovic and Murray missed the last six months of the season due to elbow and hip problems aggravated during their Wimbledon campaigns in July.
Annacone, 54, expects both players to return to their best next year but warns their fitness will be tested from the off.
"Unless there is an injury issue [Djokovic and Murray will return]," the American added. "I saw some of the Andy-Roger exhibition. I don't know how healthy Novak is, I'm not saying he is not I just don't know, and I don't know how healthy Andy is but as soon as you start playing three out of five sets early on, especially with their style of play.
"They're not going to be hitting a million aces getting a lot of free points. They're working hard from day one and we'll see how healthy early on they are.
"If they're healthy, they are great players. Great doesn't just stop, there is no reason why Murray and Djokovic shouldn't be right up on that platform at the top of the game with Federer and Nadal next year."