After their second defeat of the season - both to arch rivals Western Sydney - Corica was forced to concur the Asian Champions League commitments may take a toll on the squad.

Having not played a game in three weeks, the Sky Blues lost their opening ACL game against Yokohama F Marinos 4-0 less than a fortnight ago.

Since then, they have played another two A-League games in six days.

"I think it did take it's toll, especially the game in Yokohama. Three weeks without a game is not great," he said after their loss to Western Sydney at Netstrata Jubilee Stadium on Friday.

"You can see the sharpness of the boys over there and their intensity didn't help. We've played three games now so it should be starting to come back."

A late header from Wanderers captain Mitch Duke ended Sydney FC's 13-game undefeated streak, and handed them their second Sydney derby loss this season.

Corica maintains his team were impressive, but were undone by some bad decision making and a revived Wanderers side under caretaker coach Jean-Paul de Marigny.

"It happens sometimes. I think the last time it happened it was against them again which is not great," he said.

"A little bit of fatigue as well, mental fatigue as well from the boys after a tough week last week. I was very happy with the performance. I don't like losing but it happens sometimes.

"I think we're in a good position at the moment, we're still 13 points clear, we just wanted to be 16."

Australian Associated Press