US Open champion Dominic Thiem booked his spot in the French Open fourth round with a hard-fought 6-4 6-3 6-1 victory over Norwegian Casper Ruud.

Thiem converted six of his chances as he gradually took control en route to victory in two hours and 15 minutes.

The third seed will play 2015 champion Stanislas Wawrinka or Hugo Gaston.

"Casper is a great player - an attractive player," said Thiem.

"He has a lot of confidence and has shown he is one of the best clay-court players this year. I tried not to give him chances in the third set. "

After his three-set win over Jack Sock on Wednesday, Thiem said there would be a point at Roland Garros where he would get "super tired" - during the early stages of his match against Ruud the new Grand Slam champion was certainly breathing hard.

Thiem saved break point in his opening service game before his resistance was finally broken in the fourth game. However, the steely Austrian broke back straight away with a ferocious forehand winner.

Thiem has one of the great defences in tennis and it was severely tested in a long sixth game, where he saved three break points. Rising star Ruud, 21, then dropped a level and was broken again as Thiem went on to take the opening set.

Ruud came to Paris in great form on clay, having reached the semi-finals in Rome and Hamburg. He went toe-to-toe with his opponent during the first two sets, and produced a 'tweener' lobbed winner, which brought applause from the sparse crowd under the roof inside Court Philippe Chatrier.

However, his defence was not as strong as Thiem's and he was broken twice more in the second set before his challenge faded away in the third.