'Can't believe it': Tennis fans stunned by 'crazy' French Open drama

The tennis world was left gobsmacked on Sunday after former champion Garbine Muguruza and World No.6 Ons Jabeur crashed out of the French Open in the first round.

Jabeur became the first shock casualty on the opening day at Roland Garros, with the in-form Tunisian crashing out with a 3-6 7-6 (7-4) 7-5 loss to Poland's Magda Linette.

'TOUGH TO WATCH': Tennis stunned by 'sad' French Open moment

'ARE YOU SERIOUS': Shock Federer twist in Wimbledon furore

She was swiftly followed by two-time grand slam champion Muguruza - who won the French Open in 2016 - as the Spaniard fell at the first hurdle for the second year in a row.

She was defeated 2-6 6-3 6-4 by Kaia Kanepi of Estonia, the oldest player in the women's draw.

Coco Gauff, Maria Sakkari, Belinda Bencic and Sloane Stephens were among those to progress.

Jabeur, seen as one of the big threats to World No.1 Iga Swiatek at the clay-court grand slam, came to Paris at a career-high ranking and with a tour-leading 17 wins on the surface.

With her win at the Madrid Open and runner-up finishes in Rome and Charleston, Jabeur appeared to have an easy outing against World No.52 Linette.

The 27-year-old sixth seed breezed through the opening set in 37 minutes, but Linette staged an inspired fightback in the second, saving four break points to level via the tiebreak before winning the decider.

Jabeur's play dipped as the match went on and she made her frustration evident by kicking balls away after losing points.

"It's difficult to take that one in," Jabeur said.

"But that's what sport is like and you need to be smart enough to move forward and get back on court. So maybe it was a good thing to lose today.

"I would rather say this and be really tough with myself than waste all the good energy that I got from Madrid and Rome."

Tennis world in shock over French Open upsets

Linette said: "I had so many tough matches with Ons and last year here I lost to her in the third round so I knew how difficult it's going to be.

"She was playing so well all this time. I knew I have to be focused and play every single point and try to make her uncomfortable.

"I am happy that I just managed to fight for every single point."

Muguruza said of her disappointing form: "It's been a tough season. I've had matches so much in control, but then I don't manage to close and it gets complicated.

"But I feel that I'm training hard, I'm putting the work.

"At some point I'm a 100 per cent sure that I'm going to go out there and get those wins that have been slipping away from me."

Kanepi, who turns 37 next month, is ranked 46th and is participating in her 15th French Open.

Her best showings were quarter-final appearances in 2008 and 2012.

American teenager Gauff served 10 double-faults, faced 12 break points and was warned by the chair umpire about receiving coaching from her dad, but prevailed 7-5, 6-0 over Canadian qualifier Rebecca Marino.

with AAP

Click here to sign up to our newsletter for all the latest and breaking stories from Australia and around the world.