Three-time French Open champion Serena Williams recovered from a slow start to score a repeat win over fellow American Kristie Ahn in the first round at Roland Garros.

The pair also met in the first round of the US Open, where Williams won courtesy of a tight first set and a more comfortable second.

It was the same story here, where the 39-year-old sixth seed looked uncomfortable on the damp, slow clay in the opening set, making 28 unforced errors and having to break Ahn when she served for the set.

Williams was much improved in the tie-break, though, and did not lose a game in the second set in a 7-6 (2) 6-0 victory.

Last year's runner-up Marketa Vondrousova failed to last a round this year when she was thrashed in little more than an hour by Poland's Iga Swiatek.

The left-handed Czech, seeded 15, went down 6-1 6-2 as teenager Swiatek dominated throughout with her all-court game.

Vondrousova lost to Ash Barty in last year's final and looked in dangerous form coming in after a semi-final run in Rome.

Another notable first-round casualty was 2009 champion Svetlana Kuznetsova, the 28th seed, who was beaten in three sets by fellow Russian Anastasia Pavlyuchenkova.

Former champion Garbine Muguruza said there was no such thing as a relaxing match these days after narrowly avoiding a first-round exit when she battled for three hours to beat Slovenia's Tamara Zidansek 7-5 4-6 8-6.

The Spaniard, who reigned on the clay in 2016, looked in big trouble as she trailed 3-0 in the final set to the world number 83 but, unlike several other big names who are packing their bags, the 26-year-old survived to fight another day.

Zidansek lost her only previous main-draw match at Roland Garros but asked all sorts of questions of Muguruza who struggled to hit through a tricky opponent boasting a rock-solid defence and a nice line in disguised drop shots .

 Garbine Muguruza eventually battled through

Muguruza needed treatment for a blister on her hand at 3-4 in the final set and saved a break point in the next game.

She ended the match with 64 unforced errors but crucially played her best tennis when it mattered most, breaking the Zidansek serve at 6-6 with a crosscourt forehand winner before sealing victory on her first match point.

"Definitely the level has increased. Now everyone is more fit and prepared, and physically it's a huge difference compared to probably a decade ago," Muguruza told reporters.

"It's always like little details at the end between the great players and the good players. Especially in first rounds, you can always have surprises. There are no relaxing matches."

Czech seventh seed Petra Kvitova put in a power-packed show to beat Oceane Dodin 6-3 7-5 and breeze into the second round.

The 30-year-old twice Wimbledon champion lost only two points on serve in the opening set in her first clash with the French player, who has not got past the first round of a Grand Slam event since 2017.

Donin found her feet under the closed roof of Court Philippe Chatrier in the second set, which saw an early trade of service breaks, but Kvitova raised her game to get the break in the 11th game and close in on victory.

The Czech, who missed last year's tournament at Roland Garros due to an arm injury, sealed victory with a forehand volley for her 30th winner and will next play either Italian Jasmine Paolini or Aliona Bolsova of Spain.

Petra Kvitova made short work of  Oceane Dodin 

Fifth seed Kiki Bertens recovered from a poor start against tournament debutant Katarina Zavatska to reach the second round with a 2-6 6-2 6-0 victory.

Dutchwoman Bertens was all at sea in the first set as the 20-year-old Zavatska took advantage of her errors.

Ukraine's Zavatska needed eight set points to seal the opener but claycourt specialist Bertens, a semi-finalist here in 2016, began to shake off the rust to take the second set.

Zavatska faded in the third set and was unfortunate as she broke racket strings three times in the space of two games midway through the second set.

Bertens, who sat out the U.S. Open and retired with an Achilles injury on her return in Strasbourg last week, took full advantage and raced through the deciding set in 31 minutes.

She will play former runner-up Sara Errani in the next round after the Italian qualifier thrashed Olympic champion Monica Puig in her first Grand Slam match for two years.