When asked how Zipaway and Bustler were ahead of their group races in Melbourne on Saturday, trainer Neville Parnham's response was unequivocal.

"Both horses are absolutely thriving and have improved," Neville Parnham said.

Parnham will saddle up Zipaway in the Group 1 Australian Guineas (1600m) and Bustler in the Group 2 Blamey Stakes (1600m) at Flemington.

Zipway is an outsider in the Australian Guineas, but Parnham, a WA Racing Hall Of Fame member, will not be surprised if he caused an upset.

Parnham has never hidden his admiration for Zipaway, a horse he bred, and believes the son of Playing God has the capacity to reach the elite level.

Zipaway gave a glimpse of his potential on home soil last year when he took out the Group 2 WA Guineas (1600m) at Ascot in thrilling fashion.

He then further enhanced his growing status when finishing third behind Dom To Shoot and Zaaki in the Group 1 Northerly Stakes (1800m).

Zipaway got his first look at Melbourne racing when resuming in last fortnight's Group 2 Autumn Stakes (1400m) and ran a competitive third to Snow Patrol.

Parnham said Zipaway had improved since his first-up run and although respectful of the quality of opposition, he's confident of a top showing.

"He is doing absolutely super," Parnham told The Races WA.

"He's improvement has been out of sight.

"He's in a good space and will be better suited at a mile.

"I know he's up to quite a high level, but how high we'll know more after Saturday.

"The best is yet to come from him and I think he can really be in the picture.

"I couldn't be happier and think he'll be really competitive on the weekend.

"I think he's a fair horse and know he will run well."

In latest Tab touch betting Zipaway is rated a $15 chance behind Riff Rocket at $2.80.

He's aiming to go a couple of placings better than his boom sire Playing God who ran third to Shamrocker and Bullbars in the 2011 Australian Guineas.

Parnham is also effusive about Bustler, a Group 1 winner of the Railway Stakes (1600m) last November, bouncing back and being at his top in the Blamey Stakes.

Bustler goes into race off a last placing to Mr Brightside in the Orr Stakes (1400m) at Caulfield, unsuited by the frantic pace set up front by tough mare, Pride Of Jenni.

"It took him about a day to get over the run, but he's picked up and put on weight since," Parnham said.

"He had a good jump out last Friday and will have another good workout on Wednesday and that will do him.

"He needs to improve off his run, but the reports are he's done really well in the last couple of weeks.

"It's a blessing he's going three weeks between runs given that run (Orr) at a fast tempo took a bit out of him.

"He's in good order and both horses are thriving."

Bustler is $13 with Tab touch. Ayrton the $4.20 favourite.

Parnham's son, Steven, will ride Zipaway and Bustler.