The U's slip out of the play-off places to eighth after home defeat.
Cheltenham Town leave the JobServe Community Stadium with three points thanks to goals in either half from Alfie May and Chris Hussey.
The scoring was opened six minutes before the break when Alfie May ran clean through and slotted the ball under Gerken.
The Robins doubled their lead when Chris Hussey bent in a free kick from a tight angle twelve minutes before the end of the game.
The result drops the U’s out of the play-off places to eighth behind Port Vale who are seventh by a point.
Colchester United lined up with one change from the starting eleven that picked up three points on the road at Salford last weekend.
Brandon Comley was brought into start, with Luke Norris dropping to the bench.
It looked like Cheltenham would have to bring off the scorer of their first goal with just two minutes played, when Alfie May went down with no one around him. After a bit of treatment, he was fine to carry on.
The U’s started the brighter, looking to get at the Robins’ defence at every opportunity.
Callum Harriott had a shot in the seventh minute, but couldn’t get enough power behind the ball and it was easy for Evans to collect.
Stevenson was next to go close with a fantastic run. He picked the ball up just outside the edge of the area and ran through three visiting defenders with ease only to be denied by the visiting ‘keeper who rushed out to meet him.
It was a first half of things not quite coming off for the U’s. This was demonstrated when Harry Pell’s give and go with Theo Robinson wasn’t quite returned and cleared by the Cheltenham defence.
Cheltenham took the lead in controversial fashion, when Alfie May was very quickly one-on-one with Dean Gerken. He looked to be in an offside position, but it didn’t stop the Cheltenham forward who burst through and slotted the ball under Gerken to give his side the lead.
The U’s were left trailing at the break in a very close game.
The visitors were very close to doubling their lead six minutes into the second half, when Tozer found himself unmarked with the ball on the six-yard line, before Omar Sowunmi came across quickly to block his effort.
Theo Robinson had probably the U’s best chance of the game, when Ryan Jackson picked him out at the back post. The cross landed perfectly at his feet, but the U’s man couldn’t keep the ball down and blazed his effort over the target.
Colchester United were really going at it, but coming up short against the tightest defence in the league.
Kwame Poku cut the ball back to Ben Stevenson who was unlucky to slip just as he was about to pull the trigger from inside the area. It was a tight angle, but the U’s midfielder would have only had Evans in the Cheltenham goal to beat.
With twenty minutes to go, John McGreal looked to change things around for the U’s. He brought on both Luke Norris and Frank Nouble for Kwame Poku and Brandon Comley, but neither would be able to make an impact on the game.
Stevenson tried his luck with fifteen minutes to go from outside the area, but could only drag his shot wide of the post.
Just two minutes later and the challenge became twice as difficult when Chris Hussey bent in a free kick from a tight angle.
Luke Norris made the initial foul on the edge of the area, and it looked as though it would be a cross. Hussey caught everyone out by dipping the ball under the cross bar at the far post before running off to celebrate with the travelling fans.
The U’s tried to create something that would give them an opportunity, but it was clear to see why the Cheltenham defence have been so strong this season.
Harry Pell was allowed to shoot from outside of the area, but again, saw his effort sail over the bar.
In injury time, the Colchetser United were reduced to ten men, when Omar Sowunmi was sent off for a second bookable offence. He handled the ball when Broom was racing clear and given his marching orders by Sam Purkiss.
It was a tough day at the office for the U’s, who have now slipped out of the play-off places to eighth. Port Vale picked up a point at home to Scunthorpe, whereas Northampton beat Grimsby to move ahead of Colchester United and into the top seven.