Claycourt king Rafael Nadal overcame a wobbly start and issues with the stadium lights to subdue Italian teenager Jannik Sinner 7-5 6-3 6-0 on Monday and book a place in the French Open quarter-finals. The Spanish defending champion, looking to claim a record-extending 14th Roland Garros singles title and become the only man to win 21 Grand Slam singles crowns, has won 35 consecutive sets in Paris. World number 19 Sinner, who at 19 years old has been labelled as the next big thing in tennis, hit a brick wall on court Philippe Chatrier after leading 5-3 in the opening set. Third seed Nadal will face Diego Schwartzman for a place in the semi-finals after beating the Argentine in the last four last year. Although the sun shone throughout, part of the match was played under the floodlights. "I think the lights went on too early. The court is covered from one side. When the sun was lower and hit the light, it created shadow on the court. It was tricky," Nadal told a news conference. "Honestly, I don"t know why they put on the lights that early. We have been playing without lights here in Roland Garros forever." The 20-times Grand Slam champion still produced his best tennis when it mattered most. "I played against a very good player who has a great future and I"m very happy with the win," Nadal said. "I started playing well the first couple of games and then I played too defensive for a few games and gave him the chance to step into the court and play his shots. After that the match changed a lot." Facing the ultimate challenge on clay, Sinner struggled to get into the groove before cancelling out an early break as Nadal experienced problems with his first serve. Sinner, who lost to the claycourt master in the quarter-finals here last year, found himself up a break after two Nadal double faults and a few uncharacteristic errors. Serving for the set, however, Sinner lost the game to love and Nadal levelled at 5-5 on his opponent"s 25th unforced error before breaking to love again to seal the opening set. After losing eight games in a row, Sinner stopped the rot with a break, clinching it after rushing to the net to retrieve a drop shot and delivering a stunning crosscourt passing shot. Nadal quickly recovered to break again, however, and he served out to take a two-set lead before securing his 104th match win at Roland Garros. The Spaniard has not lost at the Paris Grand Slam tournament since 2015 when he was knocked out in the last eight by Novak Djokovic, his potential semi-final opponent.