NEW YORK -- Not even Rafael Nadal saw this coming.

In 2008, he won two Grand Slam titles and an Olympic gold medal, and finished the year ranked No. 1 in the world for the first time in his career. He won the French Open without dropping a set and beat Roger Federer at Wimbledon in a nearly five-hour marathon considered by many to be the greatest match in tennis history.

Two years later, after retiring in the quarterfinals of the Australian Open with a knee injury, Nadal won three consecutive Slams and more than $10 million in prize money.

In his final major with Toni Nadal by his side, Rafael Nadal won Grand Slam title No. 16. AFP PHOTO / Jewel SAMADJEWEL SAMAD/AFP/Getty Images

On paper, the first nine months of 2017 might not stack up against either of those seasons. This was not an Olympic year, and despite winning two Slams and making the final in three, Nadal, 31, started his year with the bitter taste of an opportunity lost in Melbourne. But 16 years into his professional career, 2017 might be his most meaningful yet.

On Sunday, Nadal beat 28th-seeded Kevin Anderson 6-3, 6-3, 6-4 to capture his 16th career Grand Slam title.

"Of course, is a very special year, no?" Nadal said afterward. "[I went] a couple of years without winning Slams, couple of years with problems. After couple of years without competing at this very high, high level, very happy to be back -- and emotional year for me.

"And as I said before, thanks to all the people that help me every day. I have a great team and a great family that supports me and believe in me, and that's a great help. Without them, of course is not impossible, but almost."

The significance of this season is impossible to sum up with a stat sheet alone. Coming off a 2016 season in which he suffered his second wrist injury in three seasons and was forced to withdraw from the French Open after the second round, Nadal's 10th win at Roland Garros in June was especially sweet. It was his first Grand Slam title since the 2014 French.

After struggling through knee pain that has followed him throughout his career, and losing in the fourth round at Wimbledon, Nadal made the quarterfinals at Cincinnati two weeks before his brilliant US Open run and regained the No. 1 ranking for the first time in more than three years.

And let's not forget the rekindling of an all-time great rivalry with Roger Federer, who won the two Slams that Nadal did not.

But what has made this season even more meaningful is that while Nadal promises to play as long as his body will allow, the most important man in his camp announced earlier this season that this will be his last.

Toni Nadal, Nadal's uncle, a former pro tennis player, has been by his nephew's side since he put a racket in Rafa's hand at age 3, coaching him through juniors and on to the ATP. Uncle Toni suggested his nephew learn the game left-handed, despite not being a natural lefty, and Rafa stuck with it.

Who Nadal would be without his uncle by his side for the past 28 years is impossible to imagine. As his peers have seen coaching change after coaching change, Uncle Toni has remained a constant in Rafael's player's box. Until now.

In February, the elder Nadal said he would step down as his nephew's coach at the end of this season to oversee the Rafa Nadal Academy in Manacor, Spain, coach the next generation of players, and spend more time with his wife and children. "That will be great for my academy, and will be great for the kids," said Toni Nadal, 57.

Entering New York, the Nadal duo knew this would be their last US Open together, the final Slam at which the younger Nadal could look up into the stands during a match and see the comforting sight of the man who taught him the game.

"Probably without him I would never be playing tennis, and it's great I had somebody like him pushing me all the time," Nadal said.

"I think because he was strong and had great motivation to practice with me since I was a kid, I have been able to get through all these problems I've had in my career in terms of injuries. That makes me stronger, and I just can say thank you very much to him, because, for sure, he's one of the most important people in my life."