Long gone are those distant days when Andy Murray was disparaged as a puny youth, insufficiently fit to go the distance or be regarded a serious competitor. For the second time in as many Grand Slam events the Scot, who now makes a habit of flexing his rapidly increasing right bicep as a demonstration of his mature strength in the moment of victory, had something truly memorable about which to roll up his sleeve.

Only the strong are capable of battling back from a two-set deficit to snatch victory. Murray had the assistance of 15,000 patriots at Wimbledon in July when he surged back from the brink of defeat against Richard Gasquet. Now he has done it again, on the same New York court at the US Open where three years ago he suffered the most embarrassing chapter of his career by throwing up on the playing surface.

Jurgen Melzer must have been hoping for a similar emission as sixth seed Murray regrouped from flirting within two points of a third-round exit. It never came. Instead the 21-year-old Scot’s fitness campaign over the past couple of years handsomely paid dividends in excruciating 85 degrees of heat and 54% humidity to register a memorable 6-7 4-6 7-6 6-1 6-3 victory.

Asked courtside immediately after his victory how he had managed to turn the match around, Murray replied: “I’m not really sure. This is why you put in all that hard work, for moments like these. He was playing unbelievably, hitting serves bang on the line, hitting his forehands huge and coming in behind it and I didn’t really get any rhythm. Once I broke him in the third set, the first time I’d broken him in the match, I started to feel a little bit better and I think that was the key.”

There was every ingredient of an unforgettable Murray match; a distinct degree of edge with his Austrian opponent who hopefully he will meet again on the grass of Wimbledon’s No 1 Court in three weeks time when the nations face off for the right to be a member of next year’s Davis Cup World Group; more than a few differences of opinion with French umpire Emmanuel Joseph; a few expletives that probably endeared him more to the New York crowd than it would the members of the All England Club; and some sublime tennis that now makes him a true contender to joust with Rafael Nadal, Roger Federer and Novak Djokovic for this title.

Murray goes forward to face the tenth seeded Swiss Stanislaus Wawrinka, who won the Olympic doubles medal alongside Federer in Beijing but has lost to the Scot three times in recent meetings.

In the previous round against another left-hander, Frenchman Michael Llodra, the British No 1’s much debated second serve seemed tentative and frankly a liability. Deciding the best method was not to put it to the test, he served admirably and allowed his opponent only the rarest of opportunities. In his first five service games, Murray allowed the Austrian just two points and continually bemused his opponent by an impressive variety of pace that resulted in Melzer hitting twice as many unforced errors.

Murray had previously beaten Melzer in a three-setter in Indian Wells five months ago but that counted for nothing as the Scot tried to maintain his mission of surpassing his quarter final finish at Wimbledon. What was more relevant against a player whose notoriously brittle self-belief had received a boost by reaching the last eight at the Olympics was to make an early impression and Murray had the upperhand for most of the first set.

Unfortunately he could not capitalise on the opportunities and a series of break point chances went to waste before the set required a tie-break and there things unravelled horrendously. Where just minutes previously he had served as well as he’d ever done, Murray now struggled to get a first ball in court and managed to win just one of six points when things were supposedly in his favour.

A succession of coaches have tried to convince Murray that overplay of the drop shot is not a good policy but in Melzer he found an opponent who uses the tactic with even more regularity. Repeatedly it proved a bad choice as Murray’s pace to the ball resulted in a succession of backhand passes but finally on set point it paid off. Once again Murray got to the ball but this time the man across the net was ready and fired the most outlandish of cross-court backhands.

Although the United States Tennis Association make a conservative $35m from the event each year, they refuse to invest in Hawk-Eye line calling technology for the third show court. Invariably it is Murray’s domain and he had cause to question the judgment of French umpire Emmanuel Joseph.

Coach Miles Maclagan and the rest of the Murray support team were treated to a verbal blast from their man as more break point chances went to waste in the second set before the slackest of games gifted Melzer a two-set lead. First Murray played the most casual of serve-and-volley combinations, then he hit a first serve a yard wide and finally a limp backhand thudded into the net. Melzer was presented with two break points and needed both but Murray again came to his aid, clipping a misjudged backhand volley wide.

Melzer, who has won just a solitary title in his career, seemed on course for a battle with Wawrinka, who recovered from a two-set deficit to beat the Italian Flavio Cipolla.

The first sign of a Murray fightback came when he converted a break point at the 10th time of trying and served for the third set at 5-4 to the good, but some outlandish play from the Austrian cancelled out the Scot’s lead and another tie- break beckoned. Once again Murray’s was the first serve to buckle but two points from defeat he decided it was time to unleash the equal-fastest timed delivery he had ever struck on the tour — a 138mph ace. Suddenly the momentum shifted, Murray took the set with a backhand drop shot followed by a pass and he was en route to another memorable victory.

One who would rather not remember his third-round effort is David Nalbandian, the seventh seed Argentine crashing out in straight sets to 32nd seed Frenchman Gael Monfils, 6-3 6-4 6-2.

Some insist Rafael Nadal is overdue a collision with that invisible wall that eventually baulks even the most durable of performers. With a third straight-sets victory in the Spaniard’s bid to add the US Open title to those of the French Open and Wimbledon as well as the Olympic gold medal, it seems the new world No 1 is not interested in anything he cannot physically see.

Nadal reached the last 16 with a 6-4 6-3 6-0 win over Viktor Troicki, who may be tipped as the next Serbian to make his presence felt near the top of the sport but clearly needs a few more lessons in Grand Slam play.

Two weeks ago Troicki proved too adept for Andy Roddick at the ATP tour event in Washington DC and reached his first final. Such an experience was a major part of the 22- year-old’s education but this was a far more testing examination. Nadal’s self-belief, after his stupendous run of success, is such that even pain does not deter him from attaining his goal.