The Reds went into half-time leading 1-0 after Dario Vidosic broke the deadlock, but surrendered the lead as Sydney netted two second-half goals to come from behind and snatch the victory.

Coolen did not hide his disappointment with the loss, suggesting there were no positives to take out of the game.

"It was a very big disappointment, not only the loss, but the way we played also ... there was nothing positive only a lot of negatives," Coolen said.

"All the things we tried were not good enough ... we did not create enough chances and we gave a lot of balls away too easy, especially in the first-half, which cost us a lot of energy.

"Fortunately they didn't score more goals, because that's what they deserved."

The Dutchman said his side did not deserve the lead they had held until Jamie Coyne's equaliser in the 60th minute, admitting Sydney were the better side.

"I didn't think it was fair we went into the change-rooms 1-0 at half-time because they created more chances than us," Coolen said.

"We tried everything we could and we couldn't get on top on them, so it was fair enough to accept that Sydney were the better team and deserved the win."

Adelaide United captain Jon McKain also shared his coach's view, describing the performance as 'rubbish'.

"To be honest I thought it was rubbish from start to finish ... no excuses, Sydney deserved the three points," McKain said.

"We didn't follow the plan that Rini wanted us to follow early on and we got ourselves in a hole we couldn't get out of. We need a bit of consistency, it's not good enough to play one week decent and the next poorly."

"We have to try and take some positives out of this game, if any, and move on, because it was a very poor performance."

Moments before Sydney's equaliser, Adelaide lost marquee signing Vidosic to a corked thigh.

The 24-year-old's absence as the link between midfield and attack was noticeable as Adelaide lacked creativity going forward, failing to break down Sydney's defence.

Coolen said losing Vidosic in the 52nd minute changed the game, especially with a limited bench that had no other attacking options.

"After losing Dario after a few minutes (into the second-half), we had to change our shape and formation ... creating some problems," Coolen said.

"In our (attacking) transition moments he is a very important player who we can get a lot of benefit out of.

"The plan was to play a bit more attacking and forward but we didn't have the attacking options on the bench."