Nadal's crown slips even as he progresses in Paris

The loss of his world No 1 ranking is looking inevitable but Rafael Nadal will not be giving up his French Open crown without a fight. The 24-year-old Spaniard, who is aiming to join Bjorn Borg as the second man in history to win the title here six times, is playing well below his best but still took his tally to 42 wins in 43 matches on these courts with his 7-5, 6-3, 6-3 victory yesterday over Ivan Ljubicic. In the quarter-finals tomorrow he will face Robin Soderling, the only man who has ever beaten him here.

Whether or not it is down to the psychological blow of losing two clay-court finals in succession to Novak Djokovic in the run-up to this tournament, Nadal has yet to find his best form. He has lost more games (53) in his first four matches than in any of his previous triumphs at Roland Garros.

"You have to be realistic and today I'm not playing enough well to win this tournament," Nadal said after yesterday's victory. "But I am in the quarter-finals again and I'm going to fight to play a better match next time. Sometimes it's much more important to win when you are not playing that well than to win when you are playing well. Winning when you are playing well is probably easier. Winning when you are not playing that well is the more difficult thing. Only the top players can do that."

Nadal went into his fourth-round encounter knowing that Djokovic is now only one win away from replacing him at the top of the rankings. Fabio Fognini's withdrawal with a leg injury from his scheduled match against Djokovic sends the 24-year-old Serb straight through to the semi-finals, in which he will face the winner of today's meeting between Roger Federer and Gaël Monfils. Just reaching the final will secure the No 1 ranking for Djokovic, even if he loses to Nadal.

If Nadal does go on to win his 10th Grand Slam title here he will have done it the hard way, even if he has won his last three matches in straight sets. There were times when he struggled against Ljubicic, though some of the credit had to go to the Croatian, who was one of only four men who had reached the fourth round without losing a set.

Djokovic will be hoping Federer and Monfils fight each other to a standstill in their quarter-final today. It will be their third meeting here in the last four years, the Swiss having beaten the Frenchman in four sets in the semi-finals in 2008 and in straight sets in the quarter-finals 12 months later.

Monfils reached the last eight by completing a 6-4, 2-6, 7-5, 1-6, 8-6 victory over David Ferrer on Court Suzanne Lenglen. The match had been called off because of bad light the previous evening with the Spaniard leading 2-0 in the fourth set. Ferrer levelled the match, clinching the set within half an hour of the resumption, but Monfils quickly composed himself in the decider.

The Parisian, roared on by his home crowd, served for the match at 5-3, only to waste two match points. Ferrer saved another match point on his own serve, but Monfils tightened the screw when the Spaniard served at 6-7, reaching 0-40 and then securing victory with a forehand winner.

Soderling, the beaten finalist here for the last two years, reached the quarter-finals with an emphatic victory over Gilles Simon, the only other Frenchman left in the competition. The Swede won 6-2, 6-3, 7-6 after two and a quarter hours.

Andy Murray went into his fourth-round match against Viktor Troicki knowing that the winner would face Juan Ignacio Chela in the quarter-finals. The Argentine beat Alejandro Falla 4-6, 6-2, 1-6, 7-6, 6-2 after nearly four hours. Chela, the world No 34, is through to his third Grand Slam quarter-final. He made the last eight here in 2004 before losing to Tim Henman and at the 2007 US Open, when he was beaten by Ferrer.