The Spaniard, playing only his second tournament following a seven-month absence with a knee injury, saw off Nalbandian 6-2 6-3 in Sao Paulo.
Nadal broke twice in the first set and recovered from 3-0 down in the second to win in one hour and 18 minutes.
He is next scheduled to play at the Mexican Open, starting on 25 February.
The 11-time Grand Slam champion has chosen to return to action on the clay courts he favours, making the final in Chile last week before losing to world number 73 Horacio Zeballos.
And while his form remained some way short of his best in Sao Paulo, the 26-year-old will be well satisfied at ending the week with his 51st tournament victory.
Nadal admitted after his semi-final that the knee was still troubling him and his movement was restricted against Nalbandian, who was making his own return from an abdominal injury in Brazil after six months out.
