By Martyn Herman
PARIS (Reuters) - Thunderclaps, rain delays, an inspired home favourite roared on by a partisan crowd -- it was all in a day's work for reigning champion Serena Williams as the world number one roared into the second week of the French Open on Saturday.
The 34-year-old American needed all her experience and tenacity to fight off France's Kristina Mladenovic 6-4 7-6(10) in an absorbing contest to set up a last-16 clash with Ukraine's Elina Svitolina who beat 2008 champion Ana Ivanovic 6-4 6-4.
There was further French disappointment later when popular sixth seed Jo-Wilfried Tsonga was forced to retire against unseeded Latvian Ernests Gulbis leading 5-2.
Tsonga, who has come closer than anyone to emulating Yannick Noah, the last home man to win the French Open in 1983, walked off with tears in his eyes after appearing to hurt his knee.
Spain's Carla Suarez Navarro, last year's semi-finalist Timea Bacsinszky and unseeded Kazakh Yulia Putintseva all booked their fourth-round spots before the rains came.
As did rising Austrian Dominic Thiem, the 13th seed, who continued his fine claycourt season to beat German teenager Alexander Zverev 6-7(4) 6-3 6-3 6-3.
The 22-year-old will face Marcel Granollers next, not more illustrious Spaniard Rafael Nadal who rocked the tournament on Friday when he withdrew because of a left wrist injury.
With Roger Federer back in Switzerland with a back injury and twice women's champion Maria Sharapova provisionally banned pending the outcome of an anti-doping hearing, the tournament is already missing some of its star turns.
So there was already tension in the air as 21-times grand slam champion Williams stepped on court to face the hard-hitting Mladenovic for the first time in her long career.
Everything seemed to be going to plan as Williams took the opening set despite some impressive play from her opponent who used the drop shot to great effect throughout.
As the sky darkened and fat rain drops began landing on the clay late in the second Williams seemed anxious to finish the contest but Mladenovic stayed strong and forced a tiebreak just at the moment the heavens opened.
When the contest resumed two and a half hours later Williams made a hash of the first few points and trailed 2-5.
She recovered to lead 6-5 but made an ugly mess of an overhead on match point, then on her second chance to close it out she walloped a forehand long after pouncing on a loopy Mladenovic drop shot that sat up begging.
Williams saved a set point with a swing volley before another match point came and went but she could finally produce her victory roar when her opponent sent a forehand wide at 10-11.
"It was very difficult today she played really well," Williams, bidding for a fourth French Open title, said.
"She forced me to play my best tennis today."
Spain's ever-reliable David Ferrer reached the last 16 for the sixth consecutive year by beating compatriot Feliciano Lopez.
Top seed Novak Djokovic was initially moved from the Court Philippe Chatrier to the smaller Suzanne Lenglen Court as organisers re-jigged the programme because of the rain, before Tsonga's misfortune sent him back to the main arena.
The Serb took to court at 7.15pm local time (1715 GMT, 1:15 PM ET) and was facing a race against the clock to beat Britain's Aljaz Bedene before light failed.
(Editing by Julien Pretot)