French Open: Serena Williams battles past Kristina Mladenovic

Defending champion Serena Williams needed five match points before downing battling French hope Kristina Mladenovic 6-4 7-6 (12-10) to reach the last 16 at Roland Garros.

The top seed, chasing a fourth Paris title and record-equalling Open era 22nd Grand Slam crown, goes on to face Ukraine's Elina Svitolina - who is coached by former French Open champion Justine Henin - for a place in the quarter-finals.

It was a tough afternoon for the 34-year-old, who needed to sit out a two-and-a-half hour rain delay before a thrilling second set tie-break - in which she had to save a set point - could commence.

Mladenovic had the set point at 9-8 in the breaker but finally wilted on a fifth match point when she went wide with a forehand.

"She played really, really well and forced me to bring out my best tennis," said Williams, the 2002, 2013 and 2015 champion.

Williams saved three break points in the ninth game of the opening set against an aggressive Mladenovic, two with aces.

The American made the 23-year-old Frenchwoman pay in the next game, racing to three set points on her way to the winning the opener.

As thunder and lightning rocked Roland Garros, Mladenovic had to save three break points in the fourth game of the second set, two more in the sixth and another in the eighth - but did so to the delight of the home crowd.

The former junior champion held on until the tie-break when torrential rain sent the players off Court Philippe Chatrier and when they finally returned, the American held her nerve.

Her sister Venus Williams is also through after she beat Alize Cornet of France 7-6 (7-5) 1-6 6-0, thus ending home hopes in the women's draw for another year.

Elsewhere Carla Suarez Navarro, the 12th seed, won a tough three-set battle with Dominika Cibulkova 6-4 3-6 6-1, and eighth seed Timea Bacsinszky beat France's Pauline Parmentier 6-4 3-6 6-1.

2008 champion Ana Ivanovic's challenge is over though - she was beaten 6-4 6-4 by Elina Svitolina.

Fifth seed Karin Knapp crashed out to Russia's Yulia Putintseva 6-1 6-1, while American Madison Keys edged past Puerto Rico's Monica Puig 7-6 6-3.

Holland's Kiki Bertens defeated tenth-seed Russian Daria Kasatkina 6-2 3-6 10-8 after a dramatic final set.