For the second time in as many weeks the Chris Waller stable has played giant killer in a Group One race at Flemington.

On the opening day of the Melbourne Cup carnival the Waller-trained Japonisme relegated the odds-on favourite Exosphere to fourth place in the Coolmore Stud Stakes.

It was the turn of Delectation to lower the colours of leading Australian sprinter Chautauqua in the Darley Classic on Saturday.

In a field that had the two previous winners of the race in Terravista and Buffering in the line-up, Delectation slipped under the radar in the lead-up to the race.

But on-course punters didn't miss out, supporting the four-year-old, ridden by James McDonald, from $18 to $14 before he scored a short-head win over Chautauqua ($1.90) with Terravista ($9.50) the same margin away third.

The Darley Classic (1200m) became an afterthought for Delectation after the gelding finished fourth in the Linlithgow Stakes on Derby day.

"It just didn't work out for him that day and we were very bullish about his chances," Waller said.

"It's deflating when you go home without winning so you look for the next chance.

"He was nominated for the race and he pulled up so well, so here we are."

Waller wasn't concerned about Delectation tackling Chautauqua after he ran second to him early last month, carrying the same weight.

He said Delectation was a difficult horse to train as he was better suited at 1400m to 1600m but didn't settle racing on a circle.

But it's a different story up the straight at Flemington.

"He only came to Melbourne with suspect form but he showed with his second to Chautauqua on Turnbull day that he's up to that level," Waller said.

"He loves the straight, so we took a chance to have a throw at the stumps."

Waller has plans to return to Royal Ascot next year and Delectation, with his liking for straight track racing, could be a part of those plans.

McDonald secured his first Group One winner for Waller who gave the jockey a lot of support after he moved to Sydney before he took up the position of No.1 rider for Godolphin in Australia.

"It's great to ride a very good horse, a very good straight horse too, in a Group One race," McDonald said.

"I'm thrilled, I'm gob-smacked that I managed to overcome those world class horses."

Dwayne Dunn, rider of the favourite, said Chautauqua tried hard but just didn't sprint as hard as he can on the soft rated track.

"He's better on top of the ground, you see that more electrifying sprint," Dunn said.

"But he toughed it out right to the wire and just missed."