Saturday was only his fourth visit to the races and he has a very low rating compared with most of the Derby hopefuls.
Purton believes the Grand Prix run can be ignored.
"Zac told Murray that he really rates the horse," said co-trainer Andrew Forsman.
"He said he got knocked around when he was just starting to make ground from fourth last at the 600m and then he got unbalanced on the home bend.
"He was impressed with the way he finished off the race."
Although 12th of 16 looks dismal on paper, Harry was only 4.3 lengths from impressive winner Upham and was running on strongly very late.
If Harry gets a Derby start it is a shame for the camp the race will this year be run on the tight Doomben track while Eagle Farm is under reconstruction. The much roomier Eagle Farm would better suit Harry's racing style.
"From what Zac said he obviously wouldn't be out of Derby contention," said Forsman.
The Baker/Forsman stable enjoyed better luck at Ellerslie, winning the first two races on the card with Gesemi and Chill Bill.
Gesemi probably promoted herself into a start in next week's $40,000 Cornwall Handicap at Ellerslie with a runaway victory in the opening race.
"Murray was talking about a Cornwall start before he left for Australia and he'll be home tonight so a decision will be made then.
"She has flown through yesterday's race and the Cornwall looks a good option for her."
Forsman stopped short of describing Chill Bill as a cheat, but declares him a horse with a mind of his own.
"He picks and chooses when he wants to try his best and things have to be going his way for that to happen. Obviously the track suited him yesterday and under a hard ride he got there."
There were mixed reactions from a pair of New Zealand trainers after Exquisite Choice and Platinum Witness ran in Saturday's Doomben Roses. Sue Walsh was delighted with the fifth placing from Exquisite Choice and Lisa Latta was disappointed after Platinum Witness finish sixth.
Both fillies got back in running and were making ground at the finish, Exquisite Choice quite strongly.
"I was rapt in her run," said Walsh. "It was her first run in five weeksand she has come through it brilliantly, she ate up everything last night.
"Jim Byrne came in and said there was no way he was getting off her for the Oaks.
"I warned him that she would go to sleep mid-race and that she'd need a good dig up to get going and he said that was exactly what happened. He said it took ages to wake her up and get her going again."
That information convinced Sue Walsh to put blinkers on the filly, something she has been considering for some time.
"The blinkers might help her to get going more quickly late in the race in the Oaks."
Platinum Witness started $2.70 favourite and was lost in her first start racing right-handed.
Damien Browne told Lisa Latta the filly continually changed strides in an attempt to get around the tight Doomben circuit.
"He said it didn't help that he couldn't find anything to lead him into the race. She came around the home bend awkwardly.
"We were disappointed but she's come through the race well and Damien will ride her again in the Oaks."
Weekend wrap
•Zac Purton believes Harry's Grand Prix run can be ignored.
•Baker/Forsman stable enjoyed better luck at Ellerslie.
•Platinum Witness disappoints in Doomben Roses.
