Add it all up and it means that there will be a first-time major title winner at the end of the tournament.
About an hour after Muguruza's exit, seven-time major champion Williams lost to 30th-seeded Timea Bacsinszky, 5-7, 6-2, 6-1 at Court Philippe Chatrier.
"She had so many answers today," said Williams, who also lost to Bacsinszky in the fourth round a year ago.
Kuznetsova, who won the 2009 French Open and 2004 US Open, was ousted by two-time major runner-up Caroline Wozniacki, 6-1, 4-6, 6-2, while 2011 US Open champion Stosur was eliminated by 19-year-old Jelena Ostapenko of Latvia, 2-6, 6-2, 6-4.
Mladenovic will face Bacsinszky next and Wozniacki meets Ostapenko.
In addition, all eight women who play in the fourth round Monday are seeking a first major title, so it will be the first French Open since 1977 - and first major tournament anywhere since the 1979 Australian Open - without a past Slam champion among the quarter-finalists.
Asked for her thoughts on the way things worked out, Williams replied: "I have no idea, it's all behind me now, so whatever happens in this tournament is not necessarily my concern anymore."
In men's action, nine-time champion Rafael Nadal and defending champion Novak Djokovic both won in straight sets to reach the quarter-finals in Paris for the 11th time, equaling Roger Federer's record for the professional era.
Next up: Nadal v No 20 Pablo Carreno Busta and Djokovic v No 6 Dominic Thiem, with the winners facing off in the semifinals.
Heading into the French Open, many figured the women's draw was wide open, because of the absences of Williams' sister, Serena (pregnant), and Maria Sharapova (denied a wild-card entry after coming off a drug suspension). How right those folks were.
This was Muguruza's first attempt at defending a Grand Slam championship and she ran into a determined Mladenovic, who was backed by a vocal crowd of compatriots chanting her nickname, Kiki, throughout the match.
Mladenovic often played to the fans, waving her arms to ask for more noise.
"I'm playing at home," Mladenovic said. "Obviously, they are excited - the atmosphere was just, yeah, amazing."
When Muguruza's complaints about the crowd were relayed to Mladenovic, she said she thought it was just as tough on her, because she had to deal with the burden of thousands counting on her to win.
"I don't think that they crossed the line," Mladenovic said. "Honestly, no, I don't think it was unsportsmanship or unfair or anything."
The last woman representing France to win the country's Grand Slam tournament was Mary Pierce in 2000.
The 24-year-old Mladenovic never had been past the third round at her home major and has never made it beyond the quarter-finals at any other.
But she managed to pull off the biggest victory of her career, despite 16 double-faults, seven in each of the last two sets on a windy day and temperatures in the teens Celsius.
"Everything wasn't perfect, there were a few concerns," joked Mladenovic. "I made about 35 double-faults today, but everything's OK!"
Muguruza, who was seeded No 4 in Paris, beat Serena Williams in the French Open final last year. She also was runner-up to the American at Wimbledon in 2015.
But the Spaniard has been repeatedly answering questions recently about whether expectations are different now that she is a major champion and whether that sort of pressure might affect her on court.
"I obviously was a little bit nervous," Muguruza said. "Through the match, I was getting more and more."
