Roger Federer again showed he cannot be discounted for this year's French Open title with a 6-1, 6-4, 6-3 hammering of 29th seed Janko Tipsarevic of Serbia in the third round in Paris, on Friday.

Much of the focus on the Paris clay has been on stuttering champion Rafael Nadal and red-hot second seed Novak Djokovic but Federer is lurking in the Roland Garros shadows ready to pounce.

The Swiss third seed was especially impressive at the net, winning five out of five exchanges in the first set when he came forward.

The only break point offered in the second set was gobbled up by the 2009 winner, who waited patiently for his chance in the third set as he looks increasingly comfortable on his least favoured surface.

Gisela Dulko, fuelled by the overnight adrenaline rush of two new family arrivals, rode a strong start to beat last year's runner-up Samantha Stosur to reach the fourth round.

Having sat by the phone in her hotel room into the early hours until her brother's twins, Myla and Teo were born, the 26-year-old unseeded Argentine was still bubbling with joy when she raced to a 4-0 lead on court Philippe Chatrier before going on to win 6-4, 1-6, 6-3.

"The key was to start well, to be aggressive from the start," Dulko told a press conference.

"Yesterday night I was awake really late. You know, it was very emotional, because I would have loved to be there, but I'm here.

"And I tried to do my best today, and that's why I did this towel for them."

"Para Myla y Teo. Valia la pena" (For Myla and Teo. It was worth it), read a towel she showed the crowd after sealing the win with a forehand winner.

Inconsistent champion Francesca Schiavone ambled into the fourth round y after China's Peng Shuai became the second player in the women's draw to suffer debilitating health problems.

The Italian was leading 6-3, 1-2 when Peng decided to pull out having been twice checked over by a doctor on court.

Peng said she had been feeling sick with a cough since Tuesday.

"It was very tough to breathe," she told reporters in a hoarse and very quiet voice.

"At the start I was OK, I took some medicine. I just need rest."

Schiavone, whose grunts got louder with every point, slipped 3-1 down in the first set but used her power rather than finesse to surge back and take a grip of the contest below cloudy skies.

The fifth seed plays former world number one Jelena Jankovic in the next round.

David Ferrer demolished Ukraine's Sergiy Stakhovsky 6-1, 6-1, 6-3 as he continued to bulldoze his way through the bottom half of the draw.

The Spanish seventh seed, who has not dropped a set in three matches, will take on either Belgian Steve Darcis or France's Gael Monfils.