World number two Andy Murray insists a patient approach was the key factor in his win over Italy’s Paolo Lorenzi at the US Open on Saturday.

The Scot, 2.50 to win the tournament, reached the last 16 at Flushing Meadows but it was the hardest victory of his week so far.

Murray made 63 unforced errors at the Arthur Ashe Stadium but he managed to find a way to secure a 7-6 (7-4) 5-7 6-2 6-3 win.

He had previously cruised past Lukas Rosol and Marcel Granollers but Lorenzi made him work for every point in a match that lasted three hours and 17 minutes.

At one point the two players exchanged a 42-shot rally but Murray believes he tried to force winners on too many occasions.

His win booked him a fourth-round meeting with Bulgaria’s Grigor Dimitrov and after Saturday’s match he admitted a more patient approach made the difference.

He told reporters: “It took me a little bit longer than I would have liked to work things out but I won, got through, and I didn’t play good so I’m happy with that. “He’s ranked 40 in the world.

He’s pretty good, so I expected a tough match. I expected long rallies. “I’m just disappointed with the amount of errors I made.

I was quite impatient at times. That cost me in the first and second sets.

“When I was more patient and waited for the right balls to go for, I played much, much better and dictated more of the points.

I wasn’t going for too much. “The unforced errors came down significantly and the winners went up.

The third and fourth sets were comfortable. Obviously the first two were extremely, extremely tough.”