Halep is bidding to become only the second Romanian woman to win a Grand Slam after 1978 French Open champion Virginia Ruzici, who is now Halep's manager and had a special ceremony on Court Philippe Chatrier earlier this week to commemorate her victory 40 years ago.
Halep had lost three of her last four meetings with Muguruza.
The Spanish 3rd seed, who was the champion in Paris in 2016, will face top seed Simona Halep for a place in Saturday's final.
Muguruza, considered the slight favourite by many, handed her serve over in the first game with a double fault on break point and Halep raced 5-0 ahead in the opening set. Sharapova suffered one of her abject losses at the Slams since her 6-3 6-0 battering at the hands of Victoria Azarenka in the 2012 Australian Open final.
A marathon ninth game proved pivotal as Halep saved three break points to pile the pressure on the third seed.
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Halep has not lost to Stephens in five years, winning the pair's past four encounters in straight sets.
Halep came agonisingly close again when she lost to Caroline Wozniacki in an Australian Open showdown in January, but has showed great character to lift herself following yet another major blow.
Not to be one who does things half-heartedly, Stephens then captured her first Premier level title at the Miami Open and won both her singles in the United States' Fed Cup semi-final victory over France.
Ahead of the French Open 2018 clash, the 23-time Grand Slam victor called out the parts related to her in Sharapova's autobiography as "hearsay". "It will be okay", she said, taking ownership of those hard moments.
The 24-year-old Spaniard stopped the rot in the sixth game before Halep quickly reasserted her authority.
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Not that Stephens - the author of one of tennis' most-successful comebacks, returning from a 11-month injury lay-off; some six weeks after her ranking had slumped to 957 clinching the US Open title - will stand by and watch.
He added: "I was not surprised [with her French Open run] at all, because I said before the tournament she was ready". "I don't want to think about that.it's a different match, different situation", she said.
While the Romanian sometimes has trouble with so much on the line, Stephens has been flawless in title matches on the WTA tour, going 6-0.
Current world number one Halep made the semi-finals for the 3rd time by battling past Germany's Angelique Kerber 6-7 (2/7), 6-3, 6-2.
Sloane Stephens may be the underdog, but she is more than capable of denying Halep once more.
Another Argentine lies in wait tomorrow in the form of Juan Martin del Potro, who beat Croatian third seed Marin Čilić 7-6, 5-7, 6-3, 7-5.
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Muguruza's big strokes overwhelmed Maria Sharapova right from the start and their quarter-final was no contest at all in a 6-2, 6-1 one-way journey. It's a grand slam final. ". Coming into this part of the year, I was losing a few first-round matches, matches that I wanted to be winning, of course".