Nadal overcame the loss of the first set to beat Nicolas Almagro 4-6 6-2 6-2, while his great rival overcame a David Ferrer fightback to win 7-5 3-6 6-3.
Nadal, who is now 14-0 on clay this season following his recent victories in Monte Carlo and Rome, moved to within one match of winning a record 18th Masters title with a battling success against his compatriot.
However, he needed to overcome a string of early errors to edge past the unseeded Almagro, eventually pulling through in two hours and 15 minutes.
The underdog had lost all five previous clashes with the second seed but capitalised on Nadal's slow start to move ahead 4-1, before saving two break points when serving for the set at 5-4.
But Nadal's groundstrokes started to find their range and with Almagro making 15 unforced errors in the second set alone, the world number three broke twice to level the match.
And the decider ended in similar fashion, Nadal breaking in the second game and easily holding his serve thereafter to book his place in the final.
"The way I was playing at the start was the way I had to play," said Almagro. "I'll have to keep working and maybe sooner or later I can manage to beat Rafa."