Halep went from out-of-sorts to on-target against Kerber, scrambling to every ball and staying the course to erase an early deficit.
Today, Sharapova suffered her heaviest defeat at the Slams since her 6-3, 6-0 battering at the hands of Victoria Azarenka in the 2012 Australian Open final.
"I have actually been told quite often that I'll never win or do well because I'm too nice of a person and I just don't have it", Keys said. 'I think there is a lot of autobiographies out in the world, especially in the sporting world, that don't necessarily speak about whether they were rivals or someone they competed against. Halep has won 12 of her last 14 matches on clay court.
The victor of Thursday's semi-final will also decide the world number one spot which Muguruza held for four weeks previous year.
Muguruza was punishing the former world No 1's second serve and broke again at the start of the second set, and although this time Sharapova hit straight back.
Halep recovered from losing the first set on a tiebreak to beat Angelique Kerber in three sets, while Muguruza enjoyed a comprehensive win over Maria Sharapova.
"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.
Sharapova didn't need to play a point in the fourth round, because Serena Williams pulled out of their much-anticipated match with an injured chest muscle.
Nadal lost the opener 6-4 against 11th-seeded Diego Schwartzman but began to play better after a rain delay of just under an hour. Halep is 3-2 in career grand slam semifinal matches. Muguruza, the 2016 French Open champion, was world number one for four weeks from September 11 to October 8 past year.
Service breaks were exchanged at the start of the second set but Muguruza is a far steelier player than four years ago and Sharapova did not get a sniff in the next five games as the Spaniard reached her fourth Grand Slam semi-final.
Two past U.S. Open champions meet in the other men's quarterfinal: No. 3 Marin Cilic against No. 5 Juan Martin del Potro. Muguruza isn't giving he opponent many chances to breathe, and that's the reason for her quick success in these recent matches.
"I think there are a lot of good things like the way my body has handled the long matches that I have played, the back-to-backs".