The Spaniard, who could drop to number four in the world if he fails to win Sunday's final and Kei Nishikori claims the silverware at the Mexican Open, booked his spot in the tournament finale courtesy of a 7-6 (7), 6-2 win over Carlos Berlocq.
Nadal looked in a spot of bother in the first set tiebreak when he fell 1-6 behind, but he recovered to win eight of the next nine points to take the opener.
The second set was a much more straightforward affair for Nadal as he broke Berlocq three times, although he did surrender one of those breaks, taking the set 6-2.
Monaco squeeze past Nicolas Almagro of Spain 6-3, 6-7 (6), 6-4 in the other semi-final, in a contest that lasted 2 hours, 28 minutes.
Should Nadal beat Monaco he will equal Guillermo Vilas' record for the most Open Era clay-court titles.