The Russian, who won the title in 2012 and lost to Serena Williams 12 months ago, recovered from a set down for the third straight match to beat 20-year-old Eugenie Bouchard 4-6 7-5 6-2 yesterday.
In the final she will face first timer Simona Halep, who has not dropped a set this tournament and defeated Andrea Petkovic 6-2 7-6 (7/4).
Sharapova is famous for her intensity and never-say-die attitude and she certainly needed that to stave off the threat of the fast-improving Bouchard.
The Canadian, who made her first slam semi-final at the Australian Open in January, took the game to Sharapova from the off and was rewarded with the first set.
Bouchard then fought back from 2-5 in the second to 5-5, helped by Sharapova twice double-faulting on set point.
But the Russian found a way eventually and, although she was not playing her best, she got the advantage in the third set and hung on to it with everything she had.
It was her 19th consecutive win in a deciding set on clay dating back to the French Open in 2010.
Sharapova said: “I don’t feel that I played my best tennis today, but to be in the semi-finals of a grand slam and winning a match where I felt my opponent played extremely well, exceptional tennis; I fought, I scrambled, and I found a way to win. I’m happy and proud about that.
“I would love to win those matches in two sets, but I always feel like I put in the work to be ready to play whatever it takes. If it takes three hours to win the match in three sets, I will be ready for that.
“If I don’t start good, if I lose the first set, I’m still going to be there until the end.”
Bouchard idolised Sharapova as a youngster but the Canadian is cut from the same cloth and it was all business on court.
Twelve months ago Bouchard played in the main draw of a grand slam for the first time and lost to Sharapova in the second round, but she is a young woman in a hurry.
She said: “I’m always disappointed with a loss. I expect a lot from myself. I felt like I was close today and just came up a bit short.
“But it just motivates me that even if I wasn’t playing great, I was still so close. That gives me extra motivation to work hard in practice and get ready for the next one and have that belief that I can do it.
“I definitely feel like I can play with the best girls in the game.”
Today, it’s the turn of the men’s semi-finals where defending champion Rafa Nadal takes on Wimbledon champion Andy Murray and Novak Djokovic faces Ernests Gulbis.
Nadal and Murray have not met in a grand slam since 2011, when they played in three successive semi-finals, the Spaniard winning them all.
That was the only previous time Murray has made the last four at Roland Garros, but Nadal knows how well the Wimbledon champion is playing on clay having come close to losing to him in Rome three weeks ago.
“Always to play against Andy is a big challenge,” he said. “Always is a pleasure at the same time. I really like him as a person. I think he’s a great guy. He always stays the same. He’s a great competitor. It’s great to have him back at his top level playing again the semi-final of a grand slam after an injury. I’m happy for him, he deserves it.
“It will be a big match and big challenge for me. I’m going to try my best. I know I have to play very well if I want to have chances to win.”