Andy Murray had every reason to flex his muscles again today after climbing into the world's top five for the first time.

Murray stormed into the quarter-finals of the US Open here in New York by destroying close friend Stanislas Wawrinka 6-1, 6-3, 6-3 under the Flushing Meadows floodlights.

It means the British No1 will now face a grudge match against Juan Martin Del Potro, the young Argentinian who aimed a ball at Murray and complained about courtside support from his mother, Judy, when they met in Rome earlier this year.

Del Potro eventually retired from that match with a back injury but there is lingering resentment over the incident and it promises to turn the quarter-final into a "must-see" battle. However, Murray's mother is not here, which removes one potential flashpoint.

Murray said he had told Del Potro at the time to "watch his mouth" and added: "My mother is one of the nicest ladies you're ever going to meet. He can say whatever he wants about me, but when you start talking about someone's family I think it's natural not to take it too well." Having been warned for swearing in Rome - which he denied - Murray was unhappy that Fergus Murphy, the umpire, took no action against Del Potro.

Murray admitted today he is not on friendly terms with his next opponent and has not spoken to him since their confrontation.

He said: "I have known Del Potro since we were really young. I wasn't great friends with him before and I don't need to be friends with him now.

"Stan, though, is one of my closest friends but when you get on the court you've got to put your emotions aside and get the job done.

"Whether I like Del Potro or not really doesn't make any difference. When you get on the tennis court it's another match, and you've got to win."

There was precious little anger or angst to be seen on centre court last night as Murray, the sixth seed, humiliated 10th seed Wawrinka and left the Swiss No2 beaten and bemused long before the crowd lost interest and headed for the exit doors.