Roger Federer continued to make heavy weather of a straightforward-looking draw at the French Open as he scraped past Nicolas Mahut 6-3 4-6 6-2 7-5 in the third round.

The Swiss struggled in patches during the match unlike top seed Novak Djokovic who raced to victory in three sets against Nicolas Devilder in the fading light.

The world number three was not expected to be troubled until a scheduled quarter-final against either Tomas Berdych or Juan Martin Del Potro but, after losing a set to unheralded Romanian Adrian Ungur in round two, he again struggled.

Federer, who has reached 31 consecutive grand slam quarter-finals, breezed through the first set against Frenchman Mahut - most famous, of course, for his Wimbledon epic against John Isner two years ago.

The 30-year-old prefers faster surfaces but he was relishing the challenge of taking on a 16-time slam champion on his home stage and the second set was competitive from the start.

When Mahut brought up his first break point in the 10th game, it was also a set point, and he took it with a searing backhand return winner down the line.

Federer looked a little flat and lacked some of his usual attacking spark but he responded in typical fashion by breaking in the third game of the third set and taking it easily.

The Swiss seemed to be on his way when, after saving a break point in the sixth game, he broke through himself at the very next opportunity.

However, Mahut responded with some fine play to break straight back and sow the seeds of doubt once more. Not for long as it turned out, Federer taking his third chance to move 6-5 ahead and this time serving it out.

Seventh seed Berdych survived a five-set examination against South Africa's Kevin Anderson to reach the fourth round of the French Open.

The Czech had lost all four of his previous five-set matches at Roland Garros but fought back from two sets to one down to triumph 6-3 4-6 6-7 (4/7) 6-4 6-4.

Both players received treatment to their thighs in the last set but it was Berdych, a possible quarter-final opponent for Federer, who secured the only break in the seventh game when Anderson served a double fault.

Meanwhile, 20th seed Marcel Granollers saved three match points before finally seeing off Tunisia's Malek Jaziri 7-6 (7/1) 3-6 6-1 3-6 7-5 in a second-round clash held over from last night.

It was the third meeting between Berdych and Anderson this year after they also clashed at the same stage of the Australian Open and in Madrid, with the Czech winning both in straight sets.

But Berdych was not surprised to be pushed hard by the 26-year-old, saying: "In Madrid he was the toughest opponent until I got to the semis.

"Today I was expecting a really, really tough one because he's coming up. He's playing well. It was a really, really close game today."

Meanwhile, Berdych also revealed he would like to work with Andy Murray's coach, Ivan Lendl, in the future.

The former Wimbledon finalist said of Lendl, a Czech by birth: "It would be an honour. But it's not only just for me to say if I want him or not. But definitely if we could be together then, of course, it could be nice."

Fifth seed Jo-Wilfried Tsonga had a more straightforward passage into the last eight, the Frenchman seeing off flamboyant Italian Fabio Fognini 7-5 6-4 6-4.

Fognini is very expressive, frequently laughing and gesturing, and Tsonga admitted he had to concentrate on staying focused.

He said: "Fabio always does that, and when I walked on the court this was one of my objectives. I didn't want to fall in the trap, because then it can become very complicated."

It was a day for long matches, with Andreas Seppi and Stanislas Wawrinka both prevailing in five sets.

Wawrinka was particularly impressive, coming from two sets to one and a break down to defeat 11th-seeded Frenchman Gilles Simon 7-5 6-7 (5/7) 6-7 (3/7) 6-3 6-2.

The Swiss player, seeded 18th, will now meet Tsonga in a repeat of their third-round clash from last year, when Wawrinka fought back from two sets to love down to win.

Seppi, meanwhile, edged out 14th seed Fernando Verdasco 7-5 3-6 6-3 4-6 6-2, while ninth seed Del Potro was impressive in a 6-3 7-6 (9/7) 6-1 victory over Marin Cilic and now meets Berdych.

Also through to the fourth round is 21-year-old Belgian Goffin, who becomes the first lucky loser to reach that stage at a grand slam since countryman Dick Norman at Wimbledon in 1995.

Goffin, who lost to Portugal's Joao Sousa in the final round of qualifying and is making his debut in the main draw at a slam, defeated Lukas Kubot 7-6 (7/4) 7-5 6-1 to set up a glamour meeting with Federer.

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