The reigning champions downed Melbourne Victory 1-0 at Etihad Stadium on Saturday with the Sky Blues featuring new signings Retre and Luke Wilkshire at the back.

And Arnold couldn't resist a sly dig at the 24-year-old's former club, Melbourne City.

“I’ve always like him as a player," the Sydney boss said of Victorian, Retre.

“For me he’s the buy of the year already - value for money and he can run well.

"Technically he’s outstanding and I was surprised he never played as much at Melbourne City as he did.

“We’re very happy to have him at Sydney.”

The Sky Blues boss said his team had a lot more to give after taking all three points courtesy of a Thomas Deng own goal.

“I think probably it was 30 per cent of our capabilities,” he said.

“It's a hell of a long pre-season and you can work as hard as you want on the training pitch but once you get into the actual action of a game it steps up the intensity.

“Normally it takes three or four rounds… it’s getting rid of the rust and we go from there but defensively we were outstanding tonight, Melbourne didn’t have a shot on goal in 90 minutes.”

Michael Zullo was rested for the Victory clash with a minor hamstring problem, but Arnold said he would be back in action on Wednesday when Sydney lock horns with South Melbourne at Lakeside in the FFA Cup semi-final.