Andy Murray produced arguably his best performance of the year to defeat Juan Martin del Potro and reach the fourth round of the French Open.

The world number one has been searching for top form all season and finally found something close to it on a cool, grey day at Roland Garros.

Murray saved four set points to win a titanic opener lasting 84 minutes and was in control thereafter to win 7-6 (10/8) 7-5 6-0.

The one significant asterisk was the fitness of Del Potro, who went into the match with a groin injury and struggled more and more as it progressed.

But Murray will have reason to feel he can be a factor at the end of this tournament after this performance, with the 30-year-old also much calmer on court.

Murray said: "I expected a very tough match. The first set was very, very important. Whoever won that set had momentum. It was very slow and heavy conditions and to be coming back was difficult.

"I thought I played some good tennis towards the end. Each day I'm feeling a little bit better and hopefully I can keep it going."

This was a brutal third-round draw. Although Murray was keen to talk up his performance in his second-round win over Martin Klizan, he surely knew he would have to significantly raise his level to stand a chance against Del Potro.

Murray and Del Potro met in two classic encounters last year. The Scot got the better of his rival to win Olympic gold before losing a five-hour marathon in the Davis Cup semi-finals.

Del Potro is still working his way back to his rightful ranking after the wrist problems that almost ended his career, and the big question was how he would pull up physically.

The Argentinian looked in trouble on Thursday before opponent Nicolas Almagro tearfully retired having aggravated a knee problem.

Del Potro's sporting reaction to an opponent in distress may have gone some way to explaining why the crowd were so much behind the Argentinian here, even cheering Murray double faults.

Del Potro's mighty forehand has survived his wrist troubles and he used it to great effect to open up a 5-3 lead in the first set.

But Murray looked much more like his old self, using the drop shot particularly well and finding the sort of penetration through the court that has been such an issue in 2017.

He saved a set point at 4-5 and then another in a memorable 10th game, missing a sitter forehand before finally breaking back.

The tie-break was a mini-match in itself, with Murray opening up a 6-4 lead, missing both set points then facing another after Del Potro pulled off a miracle forehand winner off a Murray pass.

But a double fault from the Argentinian made it 7-7 and it was Murray who took his third set point when Del Potro's forehand landed just wide.

He called for umpire Carlos Bernardes to check and stood for a good minute leaning on the net with head in hands after Bernardes admitted he could not see the mark and stuck with the line judge's call.

HawkEye - used by TV companies but not the tournament - showed that the officials were right, and Del Potro's angst surely mostly stemmed from the knowledge that with that set went his chances.

Murray broke immediately at the start of the second set but missed the chance to lead 3-0 and Del Potro, who called the doctor on court for some painkillers, stalled the Scot's progress by recovering to 5-5.

Del Potro's refusal to go away was a defining feature of their Olympic final, but this time the Argentinian's resistance proved to be fleeting.

Murray broke serve again immediately and, with Del Potro flagging, raced through the fourth set to set up a last-16 clash against either John Isner or young Russian Karen Khachanov.