The 24-year-old Spaniard, who saved two match points againstSerbia’s Viktor Troicki in the semi-finals, coasted to a straightforward 6-1, 7-5 victory over the French fifth seed.
“It’s very important for me to win a title. I want to finish the season well, and it’s a perfect way to finish the season. So I’m happy for that. I enjoy this moment, because winning a title is difficult,” said Nadal.
“I won a lot this year, but I know it’s difficult to keep winning. I’m going to try to play my best in Shanghai (next week) and the rest of the season and the Masters Cup in London, the most difficult tournament for me.
“But if I’m physically and mentally OK, I hope to keep having chances to have good matches,” he added.
Nadal promised his fans at the stadium he would return next year.
“This is my first visit here in Japan, but not the last. I will come back next year, for sure,” he said.
Nadal got off to a flying start, breaking Monfils early and taking the set with the loss of only one game.
In a tight second set neither player had a chance to break until the 11th game, when Nadal fired a service return winner to move 6-5 in front.
The Spaniard, who didn’t face a single break point against him in the 77-minute match, calmly served out for victory.
“He (Monfils) beat me in 2009 and we also had a tough match in the US Open the same year. Gael is a great player. But I played really well today. That’s the reason I won today,” said Nadal.