"After the first set I just stayed strong and didn't give up".
An anti-climactic match ended predictably, with a Sharapova backhand nestling in the net - her 27th unforced error.
The Argentine went up a break in the second set 3-2 when the rain came and delayed the match for nearly an hour.
An hour and 10 minutes later the 31-year-old was walking off after her worst French Open spanking since she managed only two games against Dominika Cibulkova at the same stage in 2009.
First, she'll have to get through the current No. 1, Simona Halep.
Simona Halep celebrates her win over Angelique Kerber. The Spaniard won the French Open in 2016 and Wimbledon previous year.
Halep now leads Caroline Wozniacki, who was eliminated in the quarters, by just five rankings points.
Play at the French Open has been called off for the day because of rain.
Kerber called for medical treatment three games into the third set, before she conceded a break, and never appeared to threaten Halep's position.
There was only one lapse, a dropped service game early in the second set, but Muguruza barely flinched before reeling off the next five games for the loss of six points.
The world number three took that setback on the chin and prowled around the court with a spring in her step as she broke again for a fourth time to lead 2-1.
But by the third set Halep had broken the German's defenses - and her resolve - as she banged in 76 percent of her first serves, with only half the unforced errors of her opponent.
It was her book "Unstoppable", published a year ago, which had dominated the build-up to her scheduled fourth-round meeting with Serena Williams, until the American pulled out injured. The two former Paris champions had not been inconvenienced by too much tennis over the past few days - Serena Williams pulled out of her clash with Sharapova while Muguruza's opponent Lesia Tsurenko lasted just two games before retiring hurt. Nadal had won 37 straight sets at Roland Garros.
Maria Sharapova hit back at Serena Williams's accusations that the Russian's autobiography was "100 percent hearsay", insisting Wednesday that controversial references to her arch-rival are accurate.
The 11th-seeded Schwartzman has never made it to the final four at any Grand Slam tournament.
On Court Suzanne Lenglen, Marin Cilic and Juan Martin del Potro were level at 5-5 in a tight first set tiebreak.
Maria Sharapova's return to the French Open came to an abrupt halt at the hands of Garbine Muguruza. The two players contested an epic three-setter at the Australian Open this year with Halep winning the decider 9-7.
Sharapova, back at the clay court slam for the first time since 2015 following a doping ban, walked on court with two French Open crowns to Muguruza's one and a 3-0 head-to-head record against the reigning Wimbledon champion.
Kerber is a two-time Grand Slam champion.