Phil Foden dominated the scoreline with a hat-trick.
Emery said: "Robin (Olsen) played well, we conceded four goals but he saved some so really good. Until the first goal we played well. We had a chance to draw the match but when they scored the third goal they showed their power. They are up there with Arsenal and Liverpool and today they confirmed it.
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"We have some injuries, we played Saturday and again this week. We have to try and save some players. We decided to do a competitive team with some young players too to get some confidence. At the end of the match we know they deserved the match they were better than us and they showed it.
"Scoring goals is good. We try for the best performances and with Jhon (Duran) we keep going.
"Focus is now Brentford. Difficult match coming up on Saturday."