He takes enormous pride in being the first Slam champion in the Murray clan and those bragging rights have helped contribute to a sparky relationship between the siblings.
For Andy, a practise session in the 90-degree heat of New York was followed by the discovery that fifth seed Nikolay Davydenko had been dumped out of the fourth round 6-4, 4-6, 6-3, 7-6 by qualifier Gilles Muller, the former junior world No1. It means that unless American Andy Roddick wins the title Murray will move up to No4 for the first time.
Former champion Roddick is a title contender having set up a quarter-final with Novak Djokovic courtesy of his 6-2, 6-4, 6-1 thrashing of Fenando Gonzalez in just 88 minutes.
Roger Federer's mistake-ridden attempt to defend his US Open title nearly fell apart against 23rd seed Igor Andreev. Although Federer found enough class to emerge a 6-7, 7-6, 6-3, 3-6, 6-3 winner he is not the same player.
Even Djokovic, the third seed, failed to live up to his billing as the Australian Open champion and he picked up hip and ankle injuries while overcoming Tommy Robredo 4-6, 6-2, 6-3, 5-7, 6-3.
The focus shifts today to Murray and the showdown between No1 seed Rafael Nadal and American Mardy Fish.
The British No1 is fired up to face Del Potro, who has attempted to defuse any lingering animosity from their last meeting in Rome, when the Argentine hit a ball at his opponent and then make remarks about Murray's mother.
Del Potro said: "It was just an emotional match. Sometimes you do something then after that you think, 'Well, I'm wrong.' I said to him, I never said anything about your mum. I don't have anything bad with Andy and when I play him I hope it's a good match." Murray is aiming to produce the same shot-making that earned a first appearance in the last eight in New York. Despite Del Potro's form in recent weeks, Murray insists he hasn't seen anything to fear from the 6ft 6in 19-year-old.
He said: "It's going to be a tough match but I believe I am playing well enough to win it. He moves pretty well for a big guy but when you watch him, I don't think you see anything that's special."
Meanwhile, the trio of British boys - Marcus Willis, Dan Smethurst and Daniel Cox - all registered wins, with Cox getting into the third round.
But Heather Watson, the only British girls' representative, lost her second round match 6-4, 6-4 to Thailand's Noppawan Lertcheewakarn, who lost to Laura Robson in the Wimbledon final.
