Wednesday

I'm staring at the triple-pack of blister cream in the “goody-bag” handed out to all caddies as they register to be a bagman in the US Open. A strange and worrying assortment of freebies, which includes an industrial-sized tub of pain-relief gel.

Is this going to be the fun experience I initially thought it might be when Gary Wolstenholme asked for a caddie? As first reserve, the veteran English amateur has been restricted to hanging around the practice areas since arriving on Saturday but eventually it was Sean O'Hair, the American, who was the victim, succumbing to a chest strain and Wolstenholme, 47, would be playing in his first US Open.

Clearly I was not his ideal choice, but matters of financial constraints led to the request; led to me standing by his 25kg tour bag; led to me wondering whether I might have been better off remaining in the media centre in my official BBC capacity, eating the occasional ice-cream and musing about Tiger and Phil.

“I have newfound respect for you, my brother,” I say, in greeting Paul Casey's sidekick, Craig Connolly, who has also spent time on the Colin Montgomerie bag and knows all there is to know about the business.

“You look like a clown,” he replies.

Thursday

This is very strange. The US media have got hold of Gary's story and the fans at Torrey Pines are aware of it. “Go Gary!” American voices yell on every hole. And our part in the heart-warming tale is not forgotten: “Yeah! B ... B ... C. Baby!” Lord Reith would be proud. I think.

Unfortunately, their plucky underdog is struggling. A short hitter, Wolstenholme is finding the length of Torrey Pines too much. All I can do is keep his clubs clean, water plentiful and work out the yardages.

Eighty-three shots have brought us to the end of the day. It looks bad, but it's far from disgraceful with most of the field struggling. I have only disgraced myself with one mis-read putt and horribly sunburnt Scottish legs.

Things can only get better...

Friday

Well, this is much worse. After a very enjoyable holed bunker shot for a birdie on the 2nd, Gary has just knifed one out of the sand on the third, over the back of the green and into the Californian jungle. A sign amid the bushes reads “Beware of snakes”. I send an elderly marshal in to hunt for the ball.

Gary's playing badly and he knows it - six over par as we walk down the 10th. I notice a large thread trailing from the bottom of his trousers. He is literally unravelling in front of me. Deftly I step on the thread, his trousers remain intact and he rolls in a 25-foot birdie putt. I am a good caddie.

It is, though, a rare moment of celebration. The 18th green brings handshakes and general commiseration.

Gary has had the great experience of a first US Open, but how he wishes he could have played better. My pain is more physical - in blister form, but they will go with that precious cream.

- Andrew Cotter is a golf commentator for BBC Radio 5 Live