The Romanian's mentality has often been questioned, but she showed her mental strength and remains on course to win her first Grand Slam.
Garbine Muguruza's big strokes overwhelmed Maria Sharapova right from the start. It was an emphatic performance for Muguruza, who made it to the fourth round of the US Open last year and just the second round of the Australian Open earlier this year.
Garbine Muguruza is coming off a straight sets win over Maria Sharapova that took 15 games to decide.
She sent down three double faults to be broken at the very start and then, after a marathon third game, found herself 3-0 down with the Spaniard finding a deep and consistent length. "When I'm talking about progression or looking back at the weeks, 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". Like, before, I gave it a lot of importance so that's why you're fighting every week, and I got there. Off the baseline, Stephens will bait Keys to go for too much, using her speed and counter-punching ability to shrink the court. "But, yeah, I think she made everyone wait a little bit".
According to ESPN Stats & Information, the last woman to win the French Open without dropping a set was Justine Henin, who did so in back-to-back years in 2006 and 2007.
Sharapova, playing at Roland Garros for the first time since 2015, suffered her most one-sided defeat at the Slams since a 6-3, 6-0 loss to Victoria Azarenka in the 2012 Australian Open final.
Sharapova and Williams were due to clash in the fourth round on Monday but the American pulled out at the last minute of their eagerly-awaited grudge match with injury.
In the other men's quarterfinal, No 3 Marin Cilic and No 5 Juan Martin del Potro were at 5-5 in a first-set tiebreaker when the matchup of past US Open champions was stopped. She double-faulted three times in the opening game, part of her 27 unforced errors.
Kerber is a two-time Grand Slam champion.
Wimbledon champion Muguruza took just 70 minutes to brush her aside 6-2, 6-1 and make the semi-finals at what is looking like one of the fortnights when she runs hot. Halep saved two match points to win that one.
No. 3 seed Muguruza professed not to know that she could overtake current world No. 1 Simona Halep of Romania by winning the Thursday semifinal. "If I do that, I will be okay after the match, no matter the result".