Old flaws are once again exposed after Murray fails to convert potential into silverware at Flushing Meadows

SINCE Andy Murray burst onto the tennis scene in 2005, it has been widely accepted that, sooner or later, he will win a grand slam title.

But as time goes by and the game's most prized silverware continues to swerve Murray's trophy cabinet, British tennis fans' most reassuring certainty is beginning to look anything but certain.

It is starting to become a case of if rather than when.

Murray's latest grand slam exit, a 7-6 (7/3) 6-7 (4/7) 3-6 3-6 defeat by Stanislas Wawrinka, was utterly dispiriting.

Any player can fail to live up to his or her potential on a given day, but to be so thoroughly outplayed by the world No 27 was nothing short of a shock.

Afterwards, Murray admitted he felt drained and physically unable to compete, something he had not experienced for "a long, long time".

"I might never win a grand slam but, if I give it 100 per cent and train and work as hard as I can, that's all I can do," he said.

Hardly the reassuring words British tennis fans were hoping for.

Perhaps had he held on to take the second set, it would have been different.

Murray initially put any physical issues down to "just part and parcel" of playing a long match, but added: "Whether it was fatigue or not I don't know. I haven't been really tired in any long matches for a long, long time. In the third and fourth sets I was struggling physically and I got frustrated with that. I haven't been in that position for a very long time.

"I felt like my chance of doing well here was slipping away. I've worked very hard to give myself a chance of winning tournaments. When I was struggling physically, I got disappointed."

But since his earliest days on the tour, when his fading towards the end of longer matches was a familiar spectacle, fitness has been one of Murray's biggest strengths.

And to see him brushed aside so easily made for uncomfortable viewing.

When the stamina issues were flagged up early in his career, he took determined action to rectify the problem, hiring a fitness team and undertaking strenuous fitness programmes in Florida at least twice a year.

The 23-year-old Scot added: "I still feel like I'm super fit, I just didn't feel great (against Wawrinka ). There were a lot of things that I was feeling on the court. But, yeah, I just haven't felt that way for a few years now.

"I'm going to have to go away and look at why that was the case and try and get better."

Murray graciously did give credit to his friend and occasional practice partner Wawrinka, however, adding: "He played better than me.

"There's not a whole lot more to it. He had a chance to win the first set and he didn't take it. I had a chance to win the second set and I didn't take it. I just struggled from then on.

"I'm very disappointed, obviously. But I think I've been more disappointed. In other grand slams, when you get closer to winning the tournament, I think it becomes a lot harder to take."

On Sunday night there were echoes of past failures not only in the way his fitness deserted him, but also in his negative demeanour and petulant rant at umpire Steve Ulrich.

What's more, he was dispatched by a player whom he beat for the loss of just seven games in his run to the final in 2008. The odds are, next time the pair meet, Murray will soundly beat the Swiss.

The odds are also that Murray will still become Britain's first male grand slam champion since Fred Perry in 1936.

But there has been a definite narrowing of the gap between what until recently looked like an almost superhuman top four – in the shape of Roger Federer, Rafael Nadal, Murray and Novak Djokovic – and the rest.

It is perfectly possible that Juan Martin Del Potro, Robin Soderling or Tomas Berdych could triumph in any given major.

Two finals will surely not be the sum total of Murray's grand slam achievements, but as time goes by life on the ATP Tour is getting harder, not easier.

Murray cannot allow himself to miss out on a slam.

Neither Greg Rusedski nor Tim Henman managed to win one. But in reaching one grand slam final and six semi-finals respectively, both could claim to have performed to the limits of their ability.

That is an achievement Murray is yet to match.