Jockey Blake Shinn has had to settle for second in a Group Three race at Flemington behind a horse trained by his family.

Shinn had ridden Pittsburgh Flyer, trained by his stepfather and stepbrother Lee and Shannon Hope, in her two spring starts but was aboard rival Dublin Lass in Thursday's G H Mumm Stakes (1100m).

Pittsburgh Flyer finished strongly under jockey James McDonald in the heavy conditions to defeat the Peter and Paul Snowden-trained Dublin Lass by a long neck with Brook Road a neck away third.

Pittsburgh Flyer and Dublin Lass finished wide apart with Dublin Lass leading in the group on the rail side of the straight course while Pittsburgh Flyer was in a group that came down the grandstand side.

Shannon Hope understood Shinn's decision to ride Dublin Lass for the successful Snowden operation.

"It was just one of those things. He's got to think of himself, not just worry about family all the time," Hope said.

Pittsburgh Flyer was sent out at $21 and had been unplaced in three wet track starts but Hope wasn't concerned about the conditions and said the addition of a tongue tie had made a difference in Thursday's race.

The mare won her only previous start down the straight in March.

"It was a great ride and the track conditions didn't really worry me," Hope said.

"She had worked very well on it at home on several occasions last preparation. We never got to see the best of her in Sydney (last campaign) as she probably got on the worst part of the track and then Hugh Bowman said he pushed the button too early."

Lee and Shannon Hope will find out on Monday if they face disqualification over elevated cobalt readings returned by three horses from their stable last year.