Deep in the bowels of the Randwick grandstand, Chris Waller told the man he famously had posters of on his bedroom walls he had made a mistake.

"We had a private chat," Waller said of his heart-to-heart with Jimmy Cassidy before he legged him aboard Grand Marshal in the Sydney Cup.

"I said, 'Jimmy, I shouldn't have forgot where I came from, should I?' Meaning I shouldn't have taken him off last start. We've both been around long enough to know he was the right jockey for today."

Cassidy will be the first to admit opportunity has dried up in recent times. And not just from Waller, one of his most loyal supporters.

The young punks in McDonald, Berry and Shinn - along with Hugh Bowman - strangle the Sydney riding market, picking and choosing who they want. The Pumper, somewhow, seemingly survives generational shift after generational shift.

"Who needs Joao Moreira and the Magic Man? We've got the Pumper," he cried on arriving back to scale with arguably the most unlikely winner in 150 years of the Sydney Cup.

And who needs the fly-in marketing machines? Especially when there is a driving finish, the elbows flailing and those flawless hands enveloped in the red gloves lifting every last ounce out of a horse seemingly with a hopeless winning chance.

This time Cassidy was doing it from behind. Waller worked his magic in the space of five days, when Grand Marshal plodded home in third behind Tremec in what many good judges described as an ordinary Chairman's Handicap.

And Cassidy did the rest, producing a withering finish to nab Grand Marshal's stablemate Who Shot Thebarman right on the line as favourite and mid-race leader Hartnell wilted in the straight.

"It is a great feeling when you come for a Sydney Cup and it is something special when the two stablemates fight it out," Waller said.

"I feel for the other owners [of Who Shot Thebarman]. I am sure they thought they had the race in the bag. Their turn will come and they will get another shot at the Melbourne Cup."

This time it was the turn of Grand Marshal's Macau-based owner CC Lai, who had won the Arrowfield Sprint earlier in the day with Delectation.

He looked skywards during the euphoric celebrations to say a little prayer after his $41 shot saluted.

It was unclear whether he was worhsipping the big man upstairs or the trainer and jockey who had seemingly worked a miracle on track. Maybe both.

"I feel very lucky with the racing colours [of red and yellow]," Lai said. "I changed my colours at first because I kept running second."

That is probably where Grand Marshal should have run.

Who Shot Thebarman looked to have the race all sewn up when Blake Shinn dashed clear, but Lai would eventually leave only his second visit to Australia with two winners rather the one he hoped.

"I got a great run and didn't go around a horse and kicked clear," Shinn said, eventually sunk by a half-head. "I thought I was the winner, but one with 52 [kilograms] just got me at the end."

The other one with 52kg was the favourite Hartnell, expected to be the closest you'll find to a living certainty on weights and measures after dropping to the feather weight after beating most of his nearest rivals at level weights in The BMW.

But Hartnell could manage only fourth as Ken Keys' roughie Like A Carousel edged into third.

"I'll never be cross on a jockey for being positive, especially on a $1.60 chance," Hartnell's trainer John O'Shea told stewards.

"He's had a seriously hard run and he seems to have recovered now. We were a bit worried about him there for a while. Look at where the horse behind him finished - 88 lengths behind the second last horse."

Which is where many thought, with tongue firmly planted in cheek, Grand Marshal might end up. He didn't, no thanks to the man who admitted he had erred when sidelining the jockey who was born to be in the thick of the action.

"I said to a lot of people in a normal Sydney Cup he would be a great chance, but this year we had two Melbourne Cup placegetters, the favourite was Hartnell who was a very impressive BMW winner and dropping in weight," Waller said.

"I was hoping the horse would stay and you just had to throw the form out the window as it was a new race."

With an old rider still up to his usual tricks.