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Dominic Samuel scored the winning goal for the Gills to see off basement boys Colchester.
Gillingham were second best in the opening half but took the lead in the second through Samuel.
That goal from the Reading loan striker was enough for the Gills, who maintained their 100% return from the festive season in a tough game against their Essex neighbours.
The Gills were also thankful to their keeper Stuart Nelson, making two fantastic late saves from Marvin Sordell.
Gills boss Justin Edinburgh made just one change to his starting XI as Max Ehmer replaced Deji Oshilaja in defence.
Gillingham were up against a Colchester team sitting bottom of League 1 with the worst defensive record in the Football League. They did, however, have a recently installed new manager.
Despite the contrasting fortunes of the two sides, it was Colchester who bossed the opening half, limiting the Gills to very few opportunities.
Rory Donnelly hit the roof of the net with a half chance and Jake Hessenthaler put one wide after getting onto the end of a Jackson cross at the back post.
That 10 minute effort for Hessenthaler was Gills’ last of the half and the longer it went on, the more likely it looked that Colchester would get their noses infront.
Five good chances in the closing stages of the half fell Colchester’s way, with George Moncur firing a free-kick narrowly wide, shortly after Gavin Massey’s shot had gone the same way.
Edinburgh made a double change at the break with Luke Norris replacing Donnelly in attack and Josh Wright being replaced by Doug Loft in midfield.
Norris didn’t have long to wait for a chance but the striker volleyed a shot into the side netting. Just before the hour mark he flicked a Dack free-kick narrowly over.
Chris Porter went close from a corner for the visitors but Norris continued to get involved, hitting a free-kick that was deflected wide.
Reading loanee Samuel put the Gills ahead with 70 minutes gone, prodding home his fourth of the season after Jackson’s cross had been helped on by John Egan.
The lead was almost doubled through Egan as his 45-yard effort rattled the bar.
It took a two super saves from Nelson to keep the lead intact, spreading himself well to deny Sordell, who headed on goal from close range off Moncur’s excellent cross.
Sordell was denied again in the last minute as Nelson saved with his feet as the striker went clean through.
Gillingham: Nelson, Jackson, Egan, Ehmer, Garmston, Wright (Loft 46mins), A Morris, Hessenthaler, Dack (McGlashan 80mins), Donnelly (Norris 46mins), Samuel. Subs not used: G Morris, Oshilaja, Osadebe, List.
Colchester: Parish, Brindley, Eastman, Elokobi, Briggs, Edwards (Garvan 80mins), Gilbey, Moncur, Massey (Harriott 76mins), Sordell, Porter (Wright 80mins). Subs not used: Barnes, Wynter, Ambrose, Bonne.
Attendance: 7,109 (345 away)