The world number five has only recently returned from a long injury break, and took longer than expected to see off the Argentinian.
The 11-time Grand Slam champion did admit afterwards that his knee had been troubling him during the semi-final.
"It was the worst day for my knee," he said. "And if the knee is not well it makes it difficult to play.
"But I am happy with the result. After seven months without playing it's good to reach the final again, even if I'm not at my best."
It is Nadal's second consecutive final appearance since his return and he will face David Nalbandian tomorrow.