The top-ranked Spaniard wasn't perfect against Murray, struggling at times with his serve and getting broken three times, but his play was consistent enough to take care of his opponent's defensive tactics.
"The conditions today were not easy," said Nadal, who saved all six break points he faced in the third set.
"Very, very difficult with the wind changing a lot." Nadal will face either 16-time Grand Slam champion Roger Federer or Novak Djokovic in the final. Federer and Djokovic, who is unbeaten in 2011, were to play in the other semifinal later Friday.
"For me it's a dream to be back in the final," Nadal said. "Both opponents will be very, very, very difficult for me and for everybody." On Saturday, defending champion Francesca Schiavone will face Li Na in the women's final.
Nadal celebrated his 25th birthday on Court Philippe Chatrier with yet another victory, improving his record on the clay in Paris to 44-1. With another victory in Sunday's final, he would equal Bjorn Borg's record of six French Open titles.
Against Murray, he certainly looked like the best player in the world.
Nadal broke Murray early in each of the three sets. And although he lost his serve once in the first and twice in the second, Nadal always looked in charge _ even helping the court crew by frequently cleaning the clay off his baseline by dragging his foot along the white paint.
When the big points were played, it was Nadal who often came out on top.
He saved 15 of 18 break points and converted six of the 13 he earned. After saving the second of two break points in the second game of the second set, Nadal let out a primal "Vamos!" or "Come on!" The wind was swirling on court yet again, at one point forcing Murray to turn around to avoid the floating red dust from getting into his eyes. A few games later, while Murray was serving in the second set, a spectator's Panama hat blew onto the clay court.
A ball boy quickly retrieved the offending chapeau, and Nadal then claimed his second break point of the game when Murray sent a backhand wide.
Three points later, Nadal broke for a 6-5 lead with a forehand winner, earning his second of five straight games.
After the match, some of his faithful fans serenaded him with a rendition of "Happy Birthday." Since opening the tournament by falling behind two sets to one against John Isner, Nadal has won 17 sets in a row.
The Spaniard's only loss at the French Open came two years ago when he was defeated by Robin Soderling in the fourth round. But he came back in 2010 and won his fifth title, beating Soderling in the final.
This year, Nadal beat Soderling in the quarterfinals.
Murray was playing his third match since injuring his right ankle in the third round. The fourth-seeded Briton, who was trying to become the first man from his country to win a Grand Slam title since 1936, said he tore a tendon when he twisted it against Michael Berrer.
But he won a five-setter in the fourth round and then won in straight sets in the quarterfinals.
He finally showed some weakness in his foot against Nadal, sighing and grabbing his ankle after wasting a break point in the final game of the first set.
"Andy is a fantastic player," Nadal said. "I think he deserves to win a Grand Slam."