Halep struck 19 winners in 60 minutes of play on Court Philippe Chatrier to return to the last eight in Paris for the second time in her career.
Pliskova will next play either No. 3 Simona Halep of Romania or No. 5 Elina Svitolina of Ukraine. "I just believed I can make it". And as Muguruza walked to the locker room after her defeat, she wagged a finger toward the stands before bursting into tears during her post-match interview.
"Now I'm happy that I can be positive on court, and I will never be negative like I was in Miami because. when I saw the video, I felt ashamed about what I did".
Yet when the match started in front of a Suzanne Lenglen court crowd that had just witnessed men's champion Novak Djokovic being routed by Dominic Thiem, Halep looked to be going out of the tournament in sympathy with the Serb.
Svitolina did not do too much wrong, with the credit going to Halep for some incredible defence and courageous play.
But she got through it - aided by a net-cord victor on her first set point in the tiebreak - and cruised in the third for a 3-6 7-6 (8-6) 6-0 win against the Ukrainian who handed Halep her lone defeat in the month of May in the Italian Open final.
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"She was my favourite to win the tournament but you look at the other players - I don't know, if Svitolina is not healthy, which I heard today she not 100 per cent (against Martic), I didn't see it".
Romanian third seed Halep trailed by a set and 5-1 against the fifth seed but somehow dug herself out of a hole before storming to victory.
French Open glory would deliver Cahill his third grand slam crown as a coach, but first since Agassi won the 2003 Australian Open after regaining the top ranking at 32.
Asked how she managed not to let the frustration take over, she said smiling: "You want me to cry, no?".
For the first time in 40 years, the women's quarter-final line-up at Roland Garros consists of no previous Grand Slam champions. She is a very good player on claycourt.
Simona Halep saved a match point on her way to the French Open semi-finals as she came back from a set and 5-1 down to beat Elina Svitolina and set up a clash with Karolina Pliskova. Halep rattled off the next five games to take a 6-5 lead, and Svitolina had to save four set points to force the frame into a tiebreaker.
Halep says: "I need to play again, because I lost that final in Rome with the injury".
- Sixth-seed Dominic Thiem leads 7-6 (5) 6-3 against defending champion Novak Djokovic after nearly two hours of play on Court Suzanne-Lenglen.