If there is a silver lining for Maria Sharapova – and she probably will not see it this way yet – then her surprise exit from the French Open on Monday may prove to be of benefit come Wimbledon.

Having reached the final at Roland Garros three years in a row, winning the title in 2012 and 2014, the defending champion fell in the fourth round, beaten 7-6, 6-4 by the Czech, Lucie Safarova. Struggling with a cold that bugged her from day one, Sharapova never managed to impose her game on the left-handed Safarova, whose wristy forehands wreaked havoc and who held her nerve to clinch arguably the biggest victory of her career.

With an extra week between the French Open and Wimbledon this year, plus the rest of this week, Sharapova will have had almost four weeks to prepare. The winner there in 2004, she has not made it past round four since 2011 – the three years when she reached the final here. Having won in Rome last month, she looked capable of winning a third French Open crown but her cold took its toll and, as she coughed and spluttered her way through the changeovers, her grip on the title slipped away.

“She was the much more aggressive player,” Sharapova said. “She took the time away from me, created her angles and I didn’t. That was the difference. I don’t like to talk about [illness or injury] and I don’t think it really makes a difference. I’m still a competitor no matter what. I was still there and I still competed but it wasn’t enough.”

The Russian will slip from No2 to No4 in the world rankings after this week and said she had still to decide whether to play a warm-up event for Wimbledon. “The most important thing is to get healthy and give myself a chance to prepare,” she said. “Whether that means a warm-up tournament or just getting extra days on grass or extra time to train physically, that’s what it will be. But by the time Wimbledon comes around, I know that I will be ready.”

For Safarova, her victory means a first French Open quarter-final and a match with Garbiñe Muguruza of Spain, the woman who put out Serena Williams here last year. Now 28, she has always had talent but injuries and nerve have occasionally let her down. Reaching the semi-finals at Wimbledon last year, she said, was the big turning point and she will go into her match with Muguruza, a 6-3, 6-4 winner over Italy’s Flavia Pennetta, full of confidence.

“I’m a bit more patient and going for my shots in the right moments,” she said. “I haven’t reached my dream yet. Many times I was very close but it didn’t happen. [But] today when a couple of match points [had gone], I was still believing I could do it. It’s very exciting.”

Serena Williams has never lacked belief and surely no one in tennis has turned around more losing situations in matches. For the third match in a row, she came from a set down, denying the young American, Sloane Stephens, 1-6, 7-5, 6-3, having looked totally out of it in a shocker of a first set.

The match, and Williams’ attitude, turned on one point, a 27-stroke rally with Williams serving at 2-3 in the second set, 15-30, prompting a huge roar. From a young age Stephens has been tipped as the heir apparent to the Williams sisters. Having beaten Venus in the first round, she was twice within three points of victory as Serena served to stay in the match at 4-5 in the second set. Williams survived to keep alive her hopes of a 20th grand slam title.

“I started out slow,” said Williams, who will play Italy’s Sara Errani in the last eight of the tournament. “I’m not sure why but it’s not how you start. It’s how you finish. Usually I’m business on and off the court. Now I’m just winning and that’s a good thing, too. There’s always room for improvement.”

The Wimbledon champion, Petra Kvitova, was another surprise loser, going out 2-6, 6-0, 6-3 to the Swiss No23 seed, Timea Bacsinszky. She will play the unseeded Belgian, Alison van Uytvanck, who beat Andreea Mitu of Romania 6-1, 6-3 to reach her first grand slam quarter-final.