It is rare enough for Chris O'Brien to be seen at a Sydney racetrack on a Saturday, let alone riding in a Group One feature.

But every now and then loyal trainers and owners call on the veteran's experience for a big race.

And he's relishing the chance to return to Randwick to partner Gosford-trained Mighty Lucky in Saturday's $1 million Epsom Handicap..

"It is always a pleasure to get back there," O'Brien said.

"The good thing about it is he likes the track as well."

Mighty Lucky will be O'Brien's third ride in the Epsom over the famous Randwick mile, 17 years after he rode Eyes To Spy who finished 15th in the final start of his career.

He was on Sincero in 2011, the horse who gave him a Group One breakthrough after 25 years of trying when he won the George Main Stakes in the lead-up to the Epsom.

O'Brien has learned a thing or two about the sort of horse that can be competitive in an Epsom.

"You really want a horse that can stay 2000 metres, which he can do," O'Brien said.

"He won the Summer Cup last year."

O'Brien was aboard the Fred Cowell-trained gelding when he finished seventh in the Group Three Bill Ritchie Handicap first-up at Randwick on September 17, a little more than a length from winner Sons Of John.

"They went a bit slow for him and he sort of got held up a bit getting to the top of the rise," O'Brien said.

"He's made good improvement out of it. He's gone ahead in leaps and bounds."

O'Brien would know, he's been riding Mighty Lucky in trackwork and the horse has continued to impress him.

"He did a bit of three- quarter gallop up the furlong and just pulled me through the saddle basically. He worked the house down."

The pair made a winning start to their association at Randwick over 1600m in April before finishing sixth in the Listed Scone Cup.

O'Brien and Mighty Lucky returned to the winner's circle in the Group Three Lord Mayor's Cup at Doomben in May.

It's a major step up for the gelding, who is the $51 outsider of the 13-horse field.

And Mighty Lucky could hardly be more appropriately named if O'Brien has success at his third Epsom attempt.