Colchester United have lost at Cambridge United and go out of this year's Checkatrade Trophy competition as a result.
After an even half hour, the hosts went ahead when Ade Azeez slipped his shot cleverly through Barnes' legs from an acute angle.
The U's keeper prevented Cambridge doubling their lead bang on half-time, saving an Azeez spot-kick and then the rebound from the same player.
U’s Head Coach John McGreal gave a debut to centre half Ollie Kensdale, who became the first player who was born in this millennium to appear for the first team.
Kensdale was one of six changes to the starting line-up, with Barnes, Prosser, Wright, MAndron and Collins to other five.
The game began with both sides having sights at goal, with Sammie Szmodics’ effort blocked at the near post and Dillon Barnes smothering a break from Jevani Brown.
The next chance fell to the hosts, but Harrison Dunk couldn’t capitalise on being judged to be onside and had his shot blocked.
Cambridge were applying a bit of pressure as the game reached the end of the first quarter, and Barnes had to be sharp at his near post to push away a Paul Lewis effort.
He couldn’t do anything on thirty three minutes though, as Azeez slipped past Frankie Kent and then drilled his shot from an acute angle through the U’s keeper’s legs to make it 1-0.
In the final few minutes of the half, the lead should have been increased but the U’s were happy with some wasteful home finishing.
Dunk volleyed well over the bar when well placed on the edge of the six yard box, and then the hosts were awarded a spot kick for a foul by Kent.
Azeez’s penalty was saved by the legs of Barnes, who then reacted superbly to push away the rebound by the same player before the ball was cleared out of the U’s danger area.
The U’s went in with just the one goal deficit, and looked the more likely side to get a goal in the early stages of the second period.
Mikael Mandron had a low shot saved, then Kent headed over the bar from a dangerous Brennan Dickenson corner.
The U’s left winger then created two chances in quick succession for Szmodics, but neither resulted in a leveller for the visitors.
First, a whipped ball into the far post looked ripe for a header from Szmodics, but the U’s youngster lookedlike he got caught in two minds and the ball was put wide by a combination of his thigh and his body.
He made a better decision for the second, controlling another far post cross before shooting goalwards – unfortunately, Dimitar Mitov pulled off a great save to preserve the Cambridge lead.
That second chance came just after the hour mark and Szmodics was replaced by Courtney Senior a couple of minutes later.
Mitov made an even better save on sixty eight minutes, changing direction in an instant to prevent an own goal after Dickenson had again caused problems down the left.
With nine minutes remaining, it looked like the hosts had made the game safe when Azeez doubled their lead.
He forced his way past Kent, who looked like he was expecting Barnes to come for the ball, and lobbed his angled effort over the helpless keeper and into the far corner.
Ryan Gondoh, who had replaced Kane Vincent-Young, tested Mitov from the edge of the box four minutes later, but was denied by a decent save from the home stopper.
Mitov couldn’t prevent the U’s getting a goal back in the first of the four minutes of injury time, as Pell clipped a right foot half volley into the top corner to give the U’s late hope.
That was extinguished a minute later, when Emmanuel Osadebe calmly sidefooted home from the edge of the box to make it 3-1 and restore the two goal cushion.
That put an end to any hopes of a comeback for the U’s, who bowed out of the Checkatrade Trophy at the group stage.