Corthwaite has been named in the Reds' squad for the first time this campaign, returning after a groin injury hampered most of his pre-season, while Shin In-Seob has been dropped.

Coolen admitted he dislikes the ruling that a squad can only have three players and a reserve keeper named on the team sheet, saying he prefers to have more than three substitutes at his disposal.

The Dutchman said the Reds' solid performance against Fury meant he was reluctant to reshuffle United's defence and rush Conrthwaite back into the starting XI.

"Everybody is fit, well not everybody, but certainly more than the last couple of weeks," he said.

"Robbie Cornthwaite comes into the squad for the first time. Shin isn't there because we had to take a decision because of the rule, three players on the bench. I'm not happy with that."

"Because of the result last week, we took the decision not to change anything so we'll start with the same players like last week."

Coolen acknowledged Sydney will provide a difficult contest for Adelaide, despite the Sky Blues and defending champions yet to record a win this campaign.

He said the Reds will have to surpass their impressive performance last week to claim maximum points and admitted United's confidence is growing after a positive start which sees them undefeated so far.

"It will be a tough game, not an easy game and maybe we will have to be better than last week," he said.

"They are a good team, a real tough team and they will be back. The start wasn't so good for them but everyone knows they are a good club, they have a good coach, good players."

"We have a lot of confidence from the last couple of weeks so we have a good feeling going over there. If we play the same level and same system and the same way we played last week, we'll have plenty of opportunities to get some points there."

The Reds boss said he isn't surprised Adelaide are second on the table despite a host of regular starters missing from the line up including captain Travis Dodd, Fabian Barbiero and Nigel Boogaard.

The Dutchman admitted United's back-to-back wins had given the team confidence and said the Reds will get stronger as players return from injury and provided they stay fit.

"I think it's because of the results. If you get a few results at the start of the competition, we've had some draws, we haven't lost a game and then we started to win some games," he said.

"That gives the team a lot of confidence, and if they stay fit and no one gets injuries ... so it doesn't surprise me. It's just the start of the season, we're on a good way now but we have to do a lot of things much better than now."