However, this is usually the point in grand slams where Halep falls apart, so it's going to be interesting if the Romanian can finally close the deal on the big stage and put herself in elite company.
Muguruza has not dropped a set so far in this year's tournament as she seeks a second championship in Paris and third major trophy overall.
Thoroughly and clinically outplayed by Muguruza in every respect, Sharapova looked uncomfortable and off-balance for most of her brief stint on court and had a particularly deflating second set in which she logged two winners to 15 unforced errors.
Against Kerber, Halep stumbled out of the gate, dropping the first set in a tiebreaker.
Halep secured an early break in the second and did not relinquish it despite some fierce pressure from the two-times major victor Kerber, with one remarkable shot at the net even prompting applause from the German.
"I didn't play flat any more, more top-spin, and I made her run a little bit more", she said.
But it was the German who started the stronger, out-hitting her rival with lethal accuracy, to win the first four games as Halep struggled to find her serving rhythm and peppered the tramlines with unforced errors. I think my shots were a lot more forced. I tried to do too much.
"When you're facing somebody that also has an aggressive style of game I think it's about who takes the command, who takes the first opportunity", Muguruza said.
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But the dogged Romanian scrapped hard to turn the contest on its head to win 6-7 (2-7) 6-3 6-2 to advance to the final four.
Nadal was broken three times and lost the opening set of his quarterfinal Wednesday against 11th-seeded Diego Schwartzman of Argentina by a score of 6-4.
Sharapova, who missed the 2016 tournament because of a doping ban and a year ago after she was refused a wild card, was broken 6 times, committed 27 unforced errors and won just 5 points on her own serve in the second set.
The signs were ominous when the five-times Grand Slam champion coughed up three nervy double-faults in the opening game.
Muguruza leads Halep 3-1 head-to-head, but this is their first grand slam match-up. Sharapova was the French Open champion in 2012 and 2014; Muguruza took the trophy in 2016. Some of those matches were very defining for me.
Kerber is a two-time Grand Slam champion.
She missed several chances to go 4-1 ahead but she remained able to built the points more convincingly.
Williams withdrew shortly before the match with a pectoral muscle injury, a moment Sharapova said she found briefly startling but not destabilizing.