Nadal improved to 10-0 on clay this year and signaled he's back to dominating on his preferred surface after a series of injuries. He won the Monte Carlo Masters two weeks ago to end an 11-month title drought.
"I didn't play at the level I did in Monte Carlo, but I'm still winning and that's the important thing," Nadal said. "I'm probably more happy winning without playing [my] best. It was more of a mental thing."
Nadal showed no signs of fatigue after pulling out a long three-set win over Ernests Gulbis in the semifinals a day earlier.
With the 17th Masters Series title of his career, Nadal matched Andre Agassi's record. Agassi achieved the feat at age 34, while Nadal is only 23.
Top-ranked Roger Federer, who was upset by Gulbis in the second round, is second with 16 Masters Series titles.
In contrast to his emotional celebration in Monte Carlo, Nadal was comparatively subdued upon winning, simply raising his hands over his head and letting out a big smile before calmly walking to the net to shake hands with Ferrer.
This tournament is an important warmup for the French Open, which starts May 23. Nadal won four consecutive titles at Roland Garros before being stunned by Robin Soderling in the fourth round last year in Paris.
"It's important to have the motivation to want to keep improving. That's the main thing," Nadal said.
Nadal's only loss in Rome came against fellow Spaniard Juan Carlos Ferrero in the opening round two years ago, when he was slowed by a foot blister. No other player has won more than three titles at the Foro Italico.
Nadal has won his last seven meetings with Ferrer, who was playing the first Masters Series final of his career.
Ferrer indicated that he was affected by the rain.
"Maybe the court was slower and I had problems to [end] the points," Ferrer said. "Of course, Rafael had good chances in the important moments. It's difficult against him, but I'm happy with my game."
Before a bundled up crowd of 10,500 inside the tournament's new stadium, both players had to deal with a slippery court and swirling winds.
Nadal applied pressure from the start and at 2-2 in the first set Ferrer had to save five break points with some uncharacteristic attacking play, going for outright winners to the corners.
Midway through the first set, Nadal won a spectacular point that included a behind-the-back shot from Ferrer.
The match was suspended for an hour because of rain with Ferrer serving at 4-4 in the first set. Ferrer maintained his concentration when the players came back out and held serve to take a 5-4 lead, but Nadal broke Ferrer's next service game when Ferrer's forehand clipped the top of the net to end a long rally.
Nadal didn't face a break point until he served for the first set and saved it with a well-positioned serve out wide that Ferrer returned long. On the next point, Nadal moved Ferrer from corner to corner and then rushed forward for an easy volley put away.
On his first set point, Nadal hit another solid first serve and Ferrer's reply sailed long.
Nadal broke again in the third game of the second set, and the match was suspended again for 1 hour, 45 minutes -- prompting many fans to head home. When the players came out again, Ferrer hit a costly double-fault and followed that with a loose forehand wide to hand Nadal another break and let him serve out the match.
Nadal finished with 24 winners to Ferrer's 15, and had 13 fewer unforced errors.
Ferrer had five double-faults, while Nadal had none. He won only 39 percent of the points on his second serve to Nadal's 67 percent.
Nadal collected the winner's check of $578,000.