Gaël Monfils broke into an impromptu dance from the rap single, Crank That; Andy Murray flourished his ever-more defined right bicep. There are different ways of celebrating momentous grand-slam tournament victories and, while one may yearn for the day Murray offers a throwback from The White Heather Club, we will happily rejoice in more muscle-flexing between now and next weekend.

Murray's section of the US Open draw has suddenly offered up the enticing prospect of a grand-slam tournament semi-final debutant. For the Scot, Stanislas Wawrinka, his Swiss opponent in the fourth round, and the two players grouped with them, the lanky Juan Martín Del Potro, of Argentina - he has won four tournaments and 22 matches in succession - and Kei Nishikori, of Japan, astonishing opportunity knocks.

Murray, the No6 seed for whom a place inside the top five beckons with the results here, is the highest ranked of the four, so expectation mounts. First, he has to take care of Wawrinka, enjoying his stand-out season as a professional, having become a top-ten player for the first time and clinching Olympic gold in the doubles competition with Roger Federer. At the end of that final, as Wawrinka lay prone, Federer indulged in what appeared to be an attempt at levitation on his partner, explaining later that he had been trying to extract the magic from Wawrinka, who had been “on fire”.

It is up to Murray to douse the blaze and the British No1 knows he cannot do so if he flirts with the inconsistencies that marked passages against Michael Llodra in the second round and, on Saturday, when he stood within two points of a straight-sets defeat by Jürgen Melzer, the Austrian. At 5-5 in the third-set tie-break, staring at a defeat that would have been hard to digest, he unleashed a fire-filled 138mph serve, his fastest on tour, supplemented by a brilliant backhand pass winner after which he stood as if posing for a sculpture.

Murray's 6-7, 4-6, 7-6, 6-1, 6-3 victory over Melzer extended his record in five-set matches to 8-4, further evidence of the maturing process, both as player and person. Wawrinka's record is an even more exceptional 10-4 and his victory over Flavio Cipolla, a lucky loser from Italy, was the fourth time that he had recovered from two sets down to win in five. And beneath that choir-boy appearance lurks a hardening attitude, for Cipolla refused to shake hands with Wawrinka at the end of the match, claiming that his opponent had reacted to his double faults with cries of “C'mon”. It could be a feisty encounter against Murray.

They have met four times this year, Murray winning all three of the matches on hard courts, so that bodes well for British prospects. Murray does not believe that 3hr 48min of frenetic tennis against Melzer will hinder him. There is not even a doubt in one's mind now that he will seize up, or throw up. “The criticism I had before was unfair. I don't think so, I know so,” he said. “When you are 18 years old, you aren't physically at your peak and it [grand-slam tennis] came on me very quickly, about two weeks after I was playing in the [ATP] Futures.

“Not only was the physical aspect tough, but mentally you can tire yourself out because you're nervous and pumped up at the same time. Everyone takes time to develop physically and though [Rafael] Nadal is a bit of an exception, even he tired at times, like in the Miami final of 2005 when he led Federer by two sets to one and lost in five.”

All those 400-metres repetitions - 70 seconds on, 70 seconds off - come to their fruition when, after so long spent on the court that it is clear that another couple of hours would not do Murray irreparable harm, hence the flexing of muscles. A local reporter was tempted to ask whether he had spinach in his diet, organic or otherwise. Murray smiled shyly.

Monfils, the explosive talent from France, broke into his flash-dance after a straight-sets victory over David Nalbandian, of Argentina, which tees up a fourth-round meeting against Mardy Fish, of the United States. There is something indefinable about the Parisian, who turns 22 today, which makes one hope he goes all the way in the game. “I want to be the best on every point, so sometimes I can go too far,” he said. “And I love to do a show, because when I was 9, 11, to play in front of a lot of people, it's something amazing. It's fun. I have to show them I am enjoying being on the court, that I enjoy my sport.”