Serena Williams suffered her earliest grand slam defeat for six years with a third-round loss against fellow American Sofia Kenin.

Not since a defeat in the same round against Alize Cornet at Wimbledon in 2013 has Williams been beaten before the quarter-finals at one of the sport's biggest events.

Twenty-year-old Kenin may be a new name to many fans but she has had a very good year so far and refused to be overwhelmed by Williams' presence in a 6-2 7-5 victory. 

Kenin struggled to hold back tears as she said: "It's a lot of emotions. Serena's such a great player and a true champion, so all respect to her.

"Playing against Serena you've really got to fight for every point. She's such a tough player. I'm just so happy with this win."

Naomi Osaka's winning grand slam run came to an end with a straight-sets defeat by Katerina Siniakova in the third round of the French Open.

The world number one had won 16 consecutive slam matches, taking in titles at the US Open and Australian Open and two victories here.

But she had been living extremely dangerously and against Czech Siniakova, the world doubles number one and ranked 42 in singles, she could not find a way back, going down 6-4 6-2.

Osaka had lost her opening set against Anna Karolina Schmiedlova and Victoria Azarenka and the pattern continued here, with Siniakova breaking to lead 5-4 having saved seven break points.

Osaka has become the expert at digging herself out of holes but she simply could not find her form here and finished with a tally of 38 unforced errors.

The mistakes became wilder as the match wore on, Osaka looking resigned to her fate. A double fault on break point to go 5-2 down put her on the precipice, and Siniakova completed the upset to reach the fourth round at a slam for the first time in singles. 

Siniakova next faces American Madison Keys, who battled to a 6-3 6-7 (5) 6-4 victory over Anna Blinkova.

Defending champion Simona Halep eased into the fourth round of the French Open for the fifth time in the last six years with a quick win over Lesia Tsurenko.

Simona Halep is moving well

Halep dropped sets in both her first two matches and revealed after her second-round win over Magda Linette that she was struggling with sickness.

But Tsurenko offered little resistance, failing to hold her serve at all during the 55-minute contest, which Halep won 6-2 6-1. Tsurenko did not look physically fresh from the start and took a medical time-out during the second set for what appeared a left hip problem. 

Halep's next test will come against Polish debutant Iga Swiatek, who only turned 18 on Friday and continued her superb tournament by beating Olympic champion Monica Puig 0-6 6-3 6-3.

Swiatek won the girls' singles title at Wimbledon last summer.