All Roland Garros courts were covered as steady drizzle prevented second-round matches from starting at 0900GMT.

The rain started a matter of minutes before the scheduled start and showed little sign of abating to raise the prospect of a first completely washed out day since 2000.

But with spots of rain still falling around Roland Garros, the covers were removed and play got under way on the main courts at 1343GMT, a loss of nearly five hours from the day's programme.

Organisers cancelled six singles matches and 16 doubles ties, with Nadal's clash against Argentine Horacio Zeballos among the casualties. Williams, the 2002 champion, also had her contest with unseeded German Julia Goerges cancelled.

Forecasters say the rain is likely to continue intermittently for the rest of the day and plummeting temperatures have also been predicted over the weekend.

Spectators will get a 50 per cent refund if there is less than two hours of play and a full refund if there is less than one hour of play, thanks to special insurance taken out by the French tennis federation.

The 22-year-old Serb, whose career has nose-dived alarmingly since winning the title here in 2008, looked almost apologetic at times during a humbling 6-3, 6-0 loss to ruthless Russian Alisa Kleybanova in 66 minutes.

A few of the fans who had waited patiently for the rain to finally stop on Court One tried to lift her but after slashing another errant forehand into the net she appeared relieved to be heading back to the privacy of the locker room.

The contrast to two years ago could not have been more stark.

Then, as the sun beat down, Ivanovic stood smiling on centre court as she held aloft the Suzanne Lenglen Cup after defeating Dinara Safina 6-3, 6-4 in the final.

That fortnight the winners flowed off her racket and she sliced through the draw for the loss of just one set. Not only did she win what many believed would be the first of many grand slam titles she also climbed to the top of the WTA rankings.

Blessed with model looks and a friendly demeanour she was a dream for the WTA Tour's marketing chiefs looking for the next pin-up to sell the women's game to the sponsors.

Things soon began to turn sour though and an early loss at Wimbledon was followed by a thumb injury that ruled her out of the Olympic Games in Beijing on the eve of the tournament.

By the end of 2009 she had dropped to 22 in the rankings and arrived at Roland Garros this year a further 20 places down the ladder despite recently hiring Steffi Graf's former long-term coach Heinz Gunthardt.

Ivanovic still managed to smile when she faced the media on Thursday but the sparkle was missing from her eyes.

"You know I love this tournament," she told reporters. "It's still my favorite tournament. I think I'm on the right path and I'm doing lots of things right.

"It's been such a long time until I was actually competing and playing lots of matches. It's gonna take some time for it to become a pattern and just being used to competing again at that high level against top players."

"Some days it might be there, some days it might not."

It definitely was not there on Thursday despite winning the first two games of the match.

From that moment on she simply could not cope with an aggressive opponent who showed no mercy but who offered some words of sympathy afterwards.

"She is obviously trying to come back but it will take time," Kleybanova, the 28th seed, said.

"Tennis is so difficult because everybody is improving. She used to be world number one, grand slam winner and everybody is looking up to you and that's difficult when things aren't going very well.

"I'm pretty sure she's strong enough though and she will keep trying. She won some matches in Rome recently and I'm pretty sure she can do it."

Elena Dementieva struggled in her second round match.

The Russian, a finalist at Roland Garros in 2004, struggled against Spaniard Anabel Medina Garriques before prevailing 6-2. 7-6 (3).

The fifth seed is still seeking her first major crown.

The fourth seed, twice a semi-finalist at Roland Garros, breezed through the first set in a buttercup yellow dress but she withered in the second set as Kanepi levelled the match.

Rain returned early in the third set, causing a 55-minute delay, but Jankovic managed to wrap up the win after two hours and four minutes when Kanepi sent a forehand long just before the tarpaulins were dragged back on to centre court.

Jankovic will next face either Ukrainian 27th seed Alona Bondarenko or Slovakia's Magdalena Rybarikova.