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Rafael Nadal expects the "toughest quarter-final of my career" against Novak Djokovic at the French Open on Wednesday.

Nine-time champion Nadal beat Jack Sock 6-3 6-1 5-7 6-2 in round four to claim a record 70th win at Roland Garros.

The Spaniard is trying to become the first player in the Open era to win 10 titles at any Grand Slam event.

Nadal has defeated Djokovic - who beat Frenchman Richard Gasquet 6-1 6-2 6-3 - six times in the French Open.

That run includes victories over the Serb in each of the past three years.

However, the Spaniard has only won one tournament since Paris last year, while top seed Djokovic is on a 26-match winning streak.

"It is not the final, you know," said Nadal, who will turn 29 on Wednesday. "It's a quarter-final. And, no, the winner of that match will not be the Roland Garros champion.

"They will be a semi-finalist of Roland Garros. That makes a big difference. Even if it's a special match, it's a quarter-final match."

Djokovic, 28, is hoping to win the one major title that has so far eluded him and thus complete the career Grand Slam.

After an impressive start against Sock, Nadal faltered as he failed to serve out the match and was broken twice in succession as the world number 30 took the third set.

But the 14-time Grand Slam champion regained control early in the fourth to win in two hours and 52 minutes.

Djokovic needed two hours to see off home favourite Gasquet, dropping serve once in the final set but breaking straight back and serving out the win.

"Of course it is a different approach mentally when you play Nadal in quarter-finals than any other player," said the Serb.

"There is no doubt about that. I'm going to try to keep my routine the same and not give so much importance to the match.

"I know what I need to do to have a chance to win. That doesn't mean that I will win. The future is unpredictable."