Spaniard Nadal, an 11-times Grand Slam champion, suffered a surprise defeat to world number 73 Horacio Zeballos last week after reaching the final in Chile.
That was his first tournament since a knee injury ruled him out of the US Open and Australian Open last year, but the world number five went one better in his second outing by easily beating the 31-year-old Argentina Nalbandian.
It was Nalbandian's first final since he was disqualified for kicking a line judge while a set up in the Queen's Club title match last June. He is now 11-13 in finals, although this was his first on clay since losing the 2008 Acapulco final to Nicolas Almagro.
The former world number one, playing only his second tournament following his return from injury, broke Nalbandian twice in the first set and recovered from 3-0 down in the second to win in 78 minutes.
It was Nadal's 51st ATP Tour title, and his fifth win against Nalbandian in seven matches.
Nadal, who said he still suffers pain in his troublesome knees, has chosen to return to action on the clay courts he favours as he tries to work his way back to match fitness.
"When the knee hurts I can't move properly," Nadal said. "And if I can't move properly, I can't hit the ball cleanly.
"When my knee gets better, the tennis will get better, the head (will get better), everything will get better. Today was the day I felt best on court."
Although he was clearly a long way from his best, Nadal showed the same swashbuckle that took him to the top of the game. In a reference to his first title in Brazil in 2005, the year he burst on to the world scene, he said he hoped this win would mark a new beginning for him.
"Brazil will always be in my heart, this is the second time I have been here," he told fans after the game. "In 2005, big things started to happen for me after winning here and I hope this time again it is the start of something good."
The Spaniard is expected to play in the Mexico Open in Acapulco later this month as he prepares to defend his French Open title in May.