A couple of weeks shy of five years ago, Jason Day went to Whistling Straits in Wisconsin and dominated the United States PGA Championship, setting a new major championship record for red numbers with his 20-under par score.

He had to stave off Jordan Spieth to do it, but Day was dominant in capturing his first major after a string of near-misses in the big four events. He closed with a 67, won by three, and cried a river of tears as he embraced caddie-coach-mentor Col Swatton on the 72nd green.

Day was 27, and the world was surely his oyster. Right then and there, he looked like a five-major player at the least, and a month on, he would elevate himself to the No. 1 world ranking to tick off another accomplishment.

It is a matter of wonder that five years on, the US-based Australian can still boast just the one major as he heads back to the PGA Championship, this time at TPC Harding Park in San Francisco, beginning tonight (AEST).

It’s a glass-half-full or half-empty thing. Day has won enough to put away the tools and know that he has had a fine career by any standards. Yet by the promises that he made and the talent and work ethic that he showed as a young man, he might have had more. He has recently admitted it publicly: he feels that he has underachieved.

It’s testament to how hard golf is at that level, and it is worth considering that Day’s body has not stood up to the rigors of the game and the hours of practice that he has done to get himself to this point. Watching him pick his ball out of the hole like a 60-year-old in recent weeks tells you that.

Day won’t have a long career with a back like that. He’s 32 now and it would surprise to see him play too many more years, so his time is definitely now.

The good news is that it ‘aint over yet. Not at least going by his past three starts on the PGA Tour which have brought top-10 finishes. Two years since his last win, he comes to San Francisco as the most likely contender of all the six Australians.

Like most players at this level, he’s still tinkering; searching for the old magic. Last week, he announced that after nearly 20 years he has parted ways with Swatton and will go coachless, like his friend Tiger Woods.

He’d previously ended the caddie-player relationship with Swatton a few years ago, and he’s had a string of bagmen since.

On the surface it might be viewed as a mistake but realistically, Day is a grown man with a family and he has vast experience on the tour. He can handle himself, and maybe he needs to. The late Peter Thomson’s words about the needless obsession of the modern player to have not only coach but a team of urgers around them come to mind.

It’s instructive that at his first start since the split became public, Day played nicely at the World Golf Championship event in Memphis. Perhaps there was a lifting of the pressure after a period of uncertainty?

Virtually all professional players change coaches at some point; it is just that the Swatton-Day combination has so much meaning that it draws more attention in the public arena. Day says he wants to make changes that would not be possible under Swatton’s coaching. But he has not explained what they are.

Harding Park is the next test of where he’s at.

Day will be joined by five other Australians – Adam Scott making his tournament return, Matt Jones, Marc Leishman, Cameron Smith, Lucas Herbert – in the field this week for a major without crowds.

There are 92 of the world’s top 100 in a great field. Brooks Koepka is pitching for a third straight PGA victory.

Live coverage is via Kayo Sports from 6am Friday.

See the full PGA Championship round one tee times.