Most of these players have performed well this season when a) played in their proper positions and b) played with the first-team and not each other.
Kolarov was excellent against the rags because the rest of the team were first-teamers. Similarly, Garcia was good at Chelsea because he was played in his proper position and surrounded by first-team players. Playing a lot of second-choice players together brings all kinds of problems regarding cohesion as well as the rustiness of the individuals themselves.
The only big problem I think is Dzeko, because of his attitude rather than his ability. The lack of celebration last night, after sulking around the pitch for 90 minutes, suggests to me that we need him out of the dressing room as soon as possible. If he thinks games like last night's are beneath him, instead of an opportunity to stake a claim for a place in the first team, then he's beyond hope.