Paris - Garbine Muguruza thrashed Maria Sharapova 6-2, 6-1 to reach the French Open semi-finals on Wednesday, condemning the Russian to her worst Grand Slam defeat in more than six years.
The Spanish third seed, who was the champion in Paris in 2016, will face top seed Simona Halep for a place in Saturday's final.
That semi-final will also decide the number one spot next week.
Current world number one Halep made the semi-finals for the third time by battling past Germany's Angelique Kerber 6-7 (2/7), 6-3, 6-2.
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.
"I am very pleased to be in another final in Paris," said Muguruza who has yet to drop a set in the tournament and claimed her first win over Sharapova in four meetings.
"I was up against a great player so I had to make sure I brought my best tennis."
Sharapova, who missed the 2016 tournament because of a doping ban and last year after she was refused a wild card, was broken six times, committed 27 unforced errors and won just five points on her own serve in the second set.
It was just her fifth loss in 25 Grand Slam quarter-finals.
"To have had the victories that I have had, to have the results that I have, obviously moving a step in the right direction," said Sharapova who had made the last-eight in Madrid and semis in Rome in the run-up to Paris.
"But today was certainly not one of those steps."
Muguruza pounced on an error-plagued Sharapova start to lead 4-0 with a double break.
Sharapova never recovered from serving up three double faults in the first game.
By the end of the first set, the five-time major winner had won just eight points against the Muguruza serve and failed to carve out a single break point.
Muguruza only hit five winners in the opener which was more than enough against the erratic Russian who reached the quarter-finals for the first time in three years when old rival Serena Williams handed her an injury-enforced walkover.
Sharapova, 31, was broken in the opening game of the second set which she immediately retrieved.
However, it was just a brief respite as 24-year-old Wimbledon champion Muguruza claimed a quick double break for 4-1, backed up by a hold for 5-1.
It was all over in the next game when Sharapova sent another backhand out wide.
On Court Suzanne Lenglen, 2014 and 2017 runner-up Halep, came back from a set down for the second time in the tournament to see off 12th seed Kerber who was bidding to become the first German woman in the last-four since Steffi Graf in 1999.
Two-time major winner Kerber raced into a 4-0 lead in the first set before having to rely on a tiebreak to nudge her ahead.
However, Halep proved the steadier player in the remainder of a tie which featured a total of 99 unforced errors and 12 breaks of serve.
In Thursday's other semi-final, US Open champion Sloane Stephens will take on fellow American Madison Keys in a repeat of the 2017 final at Flushing Meadows.