However, the Spaniard's 6-3 6-1 semi-final victory over David Goffin came amid controversy following a highly-dubious first-set line call that seemed to disrupt the Belgian.
Having secured an early break, Goffin looked set to take a 4-2 lead when Nadal sent a forehand long, only for chair umpire Cedric Mourier to overrule the call after examining the wrong mark in the clay.
Unexpectedly back to deuce, Nadal eventually prevailed in a 22-point sixth game that lasted 17 minutes and nine seconds to level the first set up at 3-3.
It appeared a significant turning point as Goffin, who knocked out world number two Novak Djokovic in the previous round, won only one game thereafter.
Nadal broke for a second time to move 5-3 ahead and then held to take the first set in 57 minutes and, from then on, the 14-time grand slam winner was barely stretched.
Nadal told the ATP Tour's official website: "It's tough to believe that I'm in a final again here. It's unbelievable news for me.
"I'm able to start the clay-court season playing a final in one of the most important events of the year. It's a very special place for me and this is something that makes me feel very happy."
He now boasts an incredible 62-4 win-loss record at the Monte-Carlo Country Club and only Albert Ramos-Vinolas stands in the way of preventing his compatriot seizing his 50th clay court title and first this year.
Ramos-Vinolas, the 15th seed who defeated world number one Andy Murray in the third round, needed two hours and 16 minutes to overcome French hope Lucas Pouille 6-3 5-7 6-1.
Nadal added of his next opponent: "He's playing better than ever. He's winning huge matches during the whole week. He's playing with big confidence, with great spirit and fight, overcoming tough situations in every match and playing a high level of tennis all the time.
"I know that I need to be at my best to keep having chances, to fight for another title here. That's what I am looking for."
Despite the controversial of his loss to Nadal, Goffin looked on the bright side.
He said: "It was a beautiful tournament. I gave it my all. I'm very satisfied with what I achieved against the best players in the world on a surface that I like. It's only positive.
"I have to keep working in that direction. I think I improved this week and I know now that I can have high ambitions."
Read the original article on Eurosport: Nadal makes most of umpire error to move step closer to historic success