McGreal's men remain seventh after Hartlepool win.
Colchester produced a positive second half performance to secure the win and three points against Hartlepool United as they consolidated their spot in the play-off places.
Kurtis Guthrie scored the first and Chris Porter scored from the penalty spot for Colchester before Nathan Thomas pulled a goal back for the visitors to ensure a nervy ending for the U's.
The three points ensured that John McGreal's men go into two away games in fine fettle, but there was also some possible bad news for the U's as Guthrie was stretchered off late on to add to the number of players out with injuries in the Colchester squad.
The first half was one that produced limited chances for both sides with Colchester having slightly the better of it, but they were unable to find a breakthrough as the game was one not played at breakneck speed.
Colchester's best chance of the half came on 11 minutes when Joe Fryer did well to deny Brennan Dickenson inside the area.
The U's had a free kick in a dangerous area on the left and the initial cross fell at the feet of Sean Murray who's goalbound shot was blocked. Dickenson then latched onto the loose ball and turned the ball goalwards with a powerful effort but Fryer was alert to save and hold onto the ball.
Dickenson then had the U's second chance of the game and this time sheer persistence awarded the winger as he chased down a ball that looked to heading out of play.
The winger won the ball off the defender and cut inside to the box but his shot lacked any real power and was easy for Fryer to save.
Colchester did have the ball in the net in the 28th minute but it was ruled out for offside as Porter tucked home a cross from Richard Brindley.
The impressive Sean Murray also had a shot deflected just wide. The tricky midfielder produced quick feet that meant he could turn and shoot from 25 yards.
From the resulting corner, a mix-up from George Elokobi and Porter at the back post meant both were unable to find a decisive touch as the goal appeared open and the U's were left frustrated as it remained goalless at half time.
The second half started very much in the same way, but Colchester did find the breakthrough towards the midway stage of the second half as Kurtis Guthrie produced a bullet header from close range after Brindley put a teasing ball in from the right hand side.
Colchester somehow failed to double their lead after 73 minutes when Porter missed from close range. The energetic Murray tapped the ball around his defender in the area before drilling a cross that hit Porter before the striker turned the ball wide, as most of the ground thought a second goal had arrived.
A penalty for Colchester saw the U's double their lead in the 77th minute as Guthrie was bundled over in the box by Liam Donnelly as he latched onto a long ball through.
Porter stepped up to take the penalty and coolly converted high into the roof of the net to make it 2-0 to the U's, as they looked to have wrapped the game up.
However, Hartlepool made life tough for Colchester in the final 10 minutes as they quickly got a goal back through Thomas as he toe poked the ball into the back of the net as he advanced into the area.
A spell of constant pressure on the Colchester goal followed as Hartlepool looked to take an unlikely point and they may have done had it not been for some heroic defending.
The U's had players chucking themselves in front of numerous shots from the edge of the area to block Hartlepool's efforts, which ensured that Colchester were able to see the game out.
The win means Colchester are now just a point off Exeter in sixth place, but remain level on points with Mansfield in eighth - it's tight in the battle for the play-offs.