The horse Peter Snowden rates as his best chance of a farewell Derby win for Darley will figure in a switch of riding tactics.

Tupac Amaru, one of two Darley runners in the $2 million ATC Australian Derby at Randwick on Saturday, will be ridden much closer to the front.

Snowden says this will ensure jockey Kerrin McEvoy can give the colt his optimal chance of winning one of Australia's oldest Classics.

Snowden will also start Gallatin but he puts Tupac Amaru ahead of the last-to-first Tulloch Stakes winner.

Tupac Amaru has not figured in the finish of the Randwick or Rosehill Guineas but Snowden has seen enough in both runs to declare him a live Derby chance.

Snowden has already told stewards Tupac Amaru will be ridden forward.

"He's a nice strong horse but he gets too far back and he leaves himself with too much to do," Snowden said on Melbourne radio station RSN.

"So we are going to be a bit more positive early and have him in the first half of the field instead of the back half."

Snowden has won the South Australian Derby with Kidnapped in 2010 but recent Derbies have also been littered with close calls for the trainer who is leaving Darley at the end of the month.

His most recent near-miss was Complacent's second to Polanski in last year's Victoria Derby.

Induna was runner-up in the 2011 Victoria Derby and Retrieve third in the same race a year earlier.

Retrieve has come closest to giving Snowden an ATC Australian Derby when second to the filly Shamrocker in 2011.

Injury ruled Complacent out of the carnival before the autumn started leaving Tupac Amaru and Gallatin to fly the flag for Snowden on Saturday in the final Derby he will saddle a Darley runner.

Snowden leaves Sheikh Mohammed's organisation to form a training partnership with his son Paul.

Rosehill Guineas winner Criterion is the $3.20 favourite with Tupac Amaru at $15 and Gallatin $17.

Gallatin enhanced his prospects when he chased down Singing Flame on a heavy track in the Tulloch Stakes.

"He's good late and he got through the conditions really well (in the Tulloch) which is a plus for tomorrow," Snowden said.

"You've got to ride him the same way. He's a different horse to Tupac (Amaru) because he's got a turn of foot.

"Tupac (Amaru) is just a grinder whereas Gallatin can sprint from the back."