Nadal beat Federer 6-1 6-3 to win his seventh Rome Masters title - a perfect tune-up for the French Open.
It was a dominant display by the Spaniard, who was seeded fifth for the tournament after a seven-month injury absence from the sport.
Roger Federer finished the match with 32 unforced errors to Nadal's eight with the side-effects of a late semi-final on Saturday showing.
In the womens section, world number one Serena Williams swept Belarusian Victoria Azarenka aside 6-1, 6-3 to win the Rome Open title.
Williams broke Azarenka's serve three times in a one-sided first set and despite a tighter second set the American prevailed to stretch her career-best winning streak to 24 games.