Nadal had his work cut out for him to beat defending champion Alexander Zverev, coming back after a rain delay to win 6-1, 1-6, 6-3.
“It was an emotional final, a tough one,” Nadal said. “The rain delay at the end, I didn't think would help me but of course later it helped.”
Zverev had been seeking a clay court hat-trick in Rome after winning in Munich and Madrid.
“Next time I have to find a way to come out better after rain and play better tennis,” Zverev conceded.
“[Nadal] came out way faster and played much more aggressive than I did … It took me a very long time to get activated again and to get going and obviously it wasn’t enough time.”
The win puts Nadal back on the top of ATP rankings after being relegated second to Roger Federer following his quarter-final loss to Dominic Thiem in the Madrid Open.
“I’m having an amazing week,” he said. “It was tough losing quarter-finals [in Madrid], so to have this trophy with me again was unforgettable.
“It’s a moment to enjoy this day and then in a couple of days we are going to think about Roland Garros and be excited about it.”
Despite losing to Nadal, 21-year-old Zverev also considered himself well-positioned for the Paris tournament.
“Of course Rafa [Nadal] will be the favourite and there is no question about it,” Zverev said. “I’ll be in the other half the draw, so that’s a good thing but I’ll be match by match there and hopefully I’ll be able to play the same kind of tennis like I did in the last three weeks.”