The Spaniard beat Hyeon Chung at the Paris Masters today to ensure he will finish the year above Rodger Federer as the best player in the world.
Nadal has suffered with a number of injuries over the past two years, where he failed to even make a Grand Slam final appearance.
But he has bounced back by winning six titles in 2017 – including Roland Garros and the US Open.
And during the darker days, Nadal admitted he never dreamed of coming back as strongly as he has.
“I had periods of time that I have been injured,” Nadal said.
“I’ve had periods of time where I was not winning. And when that happened, of course I had doubts.
“But at the end of the day for me it’s not about believing in yourself.
“It’s about belief when you work.
“Then when you win, you believe in yourself.”
The belief has seen Nadal end the year as the top player for a fourth time, following successes in 2008, 2010 and 2013.
The feat is made even more incredible given he started the year ninth in the rankings.
But did he even think it would be possible to achieve the greatness he tasted in previous years?
“Of course it was not the goal (at the start of the year),” said Nadal.
“It was impossible for me to think about that when you are coming back from a tough period of time without playing tennis and with so many injuries in the last couple of years.
“But yes, here we are, it happened. And very happy of course. Means a lot, no? After almost 10 years since the first time that I finished the year with this number.”
