In a sliding doors moment, Chris O'Brien could have been working for Chris Waller instead of riding for the champion trainer.

Waller has called on O'Brien, who usually earns a living around the NSW provincial and country racetracks, to ride three horses at Rosehill on Saturday, including Lord Mayors Cup chance Beyond Thankful.

O'Brien might be an unfamiliar name on a Waller horse in a city race, but there is a lot more to the jockey-trainer relationship than it seems.

"I've known Chris for about 25 years," O'Brien said.

"He was foreman for Paddy Busuttin (in New Zealand) at the time he was thinking about setting up his own stable and he asked me if I wanted to be his foreman and stable rider."

The offer came a week too late because O'Brien had already accepted a job in Australia to ride for Domeland, a Chinese-backed syndicate with extensive racing and breeding interests at the time.

But Waller's words to the departing jockey revealed the ambition that has taken the trainer to the top of his profession.

"When I told Chris I was going to Australia, he said `see you over there'," O'Brien said.

O'Brien rode Beyond Thankful when the stayer worked to the line to finish on the heels of the placegetters in the JRA Plate at Randwick.

The run signalled to O'Brien the import was close to the form that brought Wyong Gold Cup and Newcastle Cup wins in the spring.

"My comments to Chris after the race were `I wish I had got a run going up the rise, and not down it'. I don't think I would have beat the winner (Guardini) but I think I would have given it something to chase."

O'Brien will also ride Mr Darcy and Zourkhan for Sydney's leading stable.

Zourkhan is one of the most interesting runners at Rosehill as an import who has not raced at less than 2000m in three French starts that include a win over 2800m.