I f you rule out the freak shots and the lucky breaks, the holes-in-one and the ones-in-a-million, there aren't really all that many candidates for the accolade of greatest golf shot of all time.

A strike worthy of consideration has to be executed under pressure, almost certainly in the closing stages of a major, and it has to combine skill, vision and inch-perfect execution.

And, let’s be honest, it has to have significance as well. Few Scots will ever be persuaded that any player has produced a strike finer than Sandy Lyle’s bunkered approach to the 18th at Augusta in the final round of the 1988 Masters, but how many of us would still remember that moment of magic had Lyle not kicked on to sink his birdie putt for victory a few moments later?

It is for other reasons, though, that we recall Ernie Els’s magnificent 5-iron to the water-guarded 17th green at Congressional in the final round of the 1997 US Open. It stopped just a few feet from the flag and allowed the South African to sink the birdie putt that proved decisive in earning him his second major title. From our shamelessly parochial point of view, it was the shot that meant Colin Montgomerie would go through the rest of his career without a major to his name.

Small wonder that Els should look forward to his return to the Maryland course with a certain relish. What might be more surprising is that Montgomerie, who wept openly after coming so close there 14 years ago, should have tried to qualify for this year’s event. It may not be the worst thing in the world that the Scot failed and will watch this year’s action from the safety of a Sky commentary box.

Yet things will be different for Els this time. In the intervening years, he has added a long list of victories to his cv – the 2002 Open Championship at Muirfield included – married wife Liezl and fathered two children. A few years ago, the younger of them, nine-year-old Ben, was diagnosed with autism, a consideration that has had a major bearing on Els’s work pattern since.

On the one hand, he does what he can to be at home as much as possible. On the other, he works tirelessly to raise funds to provide therapy and access to education for autistic children. He has set up a foundation, with the target of raising $30m, the first $6m of which has already come straight out of his own pocket. With his father’s riches, Ben is probably set up for life, but Els is determined that other lives should be improved as well.

All of which has only added extra fuel to the fires of speculation that have surrounded Els since he first emerged from South Africa 20 years ago. In short, a long line of commentators have claimed that Els has achieved far less in the game than his abundant gifts actually merited. To add to the oft-repeated argument that he has lacked the inner determination to become one of the greats of the sport, we now have a suggestion that his personal circumstances also act as a brake on his potential.

Thankfully, no critic has yet been so crass as to suggest that Els should have done anything other than devote himself to improving the life of his son and others like him. And even if the 41-year-old has lately taken a slide down the world rankings – he is currently 22nd – he has still managed to win a clutch of tournaments, and contended in many more, since Ben’s diagnosis a few years ago.

And yet, cod psychology apart, Els is unquestionably in the midst of one of the worst runs of form of his professional career. He ended 2010 on a high by winning the South African Open Championship, the third time he had won his own national title, but he has struggled badly since, finishing no higher than 15th in the 13 events he has played this year. Which makes his analysis of the challenges of a US Open all the more intriguing.

“It is a different way to play,” Els says. “In the US Open, if you don’t drive it on the fairway, you get nailed. If you don’t hit your second shot perfect, you get nailed. If you don’t putt well, you get nailed. On a scale of zero to 10, everything has got to be right up there. You have got to be on your game or you shouldn’t bother turning up.”

By which yardstick, the Congressional field would be very small indeed this week – and Els wouldn’t be a part of it either. Yet there he will most certainly be, teeing up in the company of Davis Love III and Jim Furyk on Thursday morning. Major winners all, but the group has an alarmingly ceremonial look about it. Furyk has done little of any note this year, while Love has dropped to 130th in the world rankings.

Els topped the FedEx Cup regular season standings last year, but he is 130th on this year’s list. Tellingly, he is in the top-10 for greens-in-regulation figures, so his results point to problems on the green. Not that any statistical analysis is required, as Els has recently taken possession of a belly putter, an item that can usually be interpreted as a declaration of desperation by any player who puts one in his bag.

It is an interesting development, not least because Els called for belly putters to be banned just a few short years ago. Needs must, though, and if the price of adopting what he calls “an old man’s stick” is, well, stick, then he’ll take it on the chin so long as it produces results.

“I feel much more comfortable,” Els says. “I am starting to smile on the course for the first time in about 10 years. It has been very frustrating. I am really going to try and refine this method of putting and see where it takes me. But I am really starting to hit it nicely and starting to play a little better.”

In American eyes, Els announced himself in golf when he won the US Open at Oakmont in 1994 (again, the runner-up was one Colin Montgomerie) although he already had two top-10 finishes at the Open Championship to his name. The American event has always seemed to bring the best out of him, and he was firmly in the frame again at last year’s event at Pebble Beach, when he finished third, two strokes back from Graeme McDowell.

In one sense, though, things will be a little different when he goes back to Congressional this week. The 17th, the scene of his wonder strike in 1997, is now the final hole, the organisers having decided that the old 18th, a par three, did not test players under pressure. Still, if he’s in the mix and a nerveless finish is what is required, you wouldn’t bet against the Big Easy coming up with the goods again.