PARIS (AFP) - Juan Martin del Potro hailed French Open conqueror Andy Murray for playing like a "real No. 1" as he slipped to a straight sets loss at the hands of the British star on Saturday (June 3).

Del Potro wasted four set points in the opening set - including one off a double fault - before Murray went on to claim a 7-6 (10/8), 7-5, 6-0 victory to reach the fourth round.

"I had great opportunities in the first two sets. Those sets were very decisive. I felt I was playing well. I could feel I was hurting him," said the 28-year-old Del Potro.

"But it still was extremely complicated, because he was starting to return the balls better. My service was not hurting him as much anymore later into the game. He is a real No. 1."

Giant Argentine Del Potro was the better player in the 86-minute opening set.

But Murray was relentless in his defence, forcing his opponent to play off his backhand which has lost much of its formidable zip following three wrist surgeries.

At the end of the first set, Del Potro slumped on the net, head down after squandering chance after chance.

He knew the opener was key in the slow, heavy conditions and by the third set, he was on the ropes, winning just 11 points.

"He played very smartly. I knew that if I stayed behind the baseline, he can only do so much. So that's why he kept forcing me to move," recognised the 29th seed.

"Then he forced me to play backhand first, and then he sliced me.

"Sometimes the balls would then go crosscourt diagonally, and only a very, very few smart players can do that.

"Andy is one of the smartest guys on the circuit." Murray, who has now defeated Del Potro seven times in 10 meetings, admitted the key to victory was to keep his opponent moving and guessing.

"I think with the conditions today, it's not easy to generate pace," said the 2016 runner-up.

"On his backhand side, he doesn't make many mistakes off that side. He's normally very, very solid on the backhand crosscourt.

"But each time I had the opportunity to move around and dictate the points with my forehand from my backhand corner.

"You need to open up the other side of the court first. It's important to get the balance right."

Murray's 28 unforced errors compared to Del Potro's 43 provided a useful illustration of where the match was won and lost.

Murray will now face either John Isner of the United States or Russia's Karen Khachanov for a quarter-final spot.