Andy Murray set up a repeat of last year’s classic Olympic final against Juan Martin Del Potro after being forced to battle into the third round of the French Open.

The world No 1 was rarely comfortable against the streaky Slovakian Martin Klizan, but fought back in the fourth set to win 6-7, 6-2, 6-2, 7-6 in a grueling three hours and 35 minutes.

Del Potro progressed when his opponent Nicolas Almagro retired in the third set with a knee injury.

“I expected it to be very tough, he goes for huge shots, he can hit winners from anywhere on the court with his forehand,” said Murray of Klizan.

“ He comes up with unbelievable power from defensive positions. When he is controlling with his forehand it’s very difficult.

“I didn’t want a fifth set but at the end there were some entertaining points, it was a great atmosphere. I try to behave as good as I can but can always improve for sure.”

Murray said of meeting Del Potro: “It will be very tough, Juan Martin plays better than his ranking. He has come back from injuries and had some tough draws this year. He is playing well but has played some good players in early rounds.”

He will need to improve against the towering Argentinian, although there were again signs that Murray’s mojo is returning.

While short of his clay form last year, and short of first serves, he held much firmer in the fourth set to clinch it with a lunging volley 7-3 against the very awkward Klizan, world No 50.