City were unable to maintain their good form in the Professional Development League South, when they suffered a defeat away at Colchester United.
It was a great start for the Under-23s, when Jordan Ponticelli gave them the lead after he headed home from a Dion Kelly-Evans cross.
However, the hosts were back on level terms a few moments later, when Courtney Senior equalised with a shot from the edge of the box.
Then, United took the lead just before half time, with Decarrey Sheriff firing home a left footed shot from the edge of the area.
After the break, Colchester extended their lead, as Senior bagged his second of the game, when he finished his effort at the near post.
City then got on back thanks to Bilal Sayoud, as the Sky Blues looked to mount the pressure on the hosts and try and get back into the game.
However, Tariq Issa ensured that Colchester would leave Florence Park with all three points, as he extended the lead, before the full-time whistle went.
Sky Blues: O'Brien, Dion Kelly-Evans, Ford, Hyam, Stokes, Maycock, Vincenti, Stevenson, Devon Kelly-Evans, Ponticelli, Sayoud
Subs: Hickman, Bayliss, Camwell, Finn, Ford