Dan Crowley's excellent opener counted for nothing as Gillingham took the points on a disappointing night.
We looked well on course for a successful evening when our strong start resulted in Jodi Jones claiming his 18th assist of the season, a Sky Bet League Two record.
But we let our control slip with the concession of two goals before the break, and another shortly after half-time, and we were unable to recover.
Stuart Maynard selected the same starting XI as he did for last weekend’s Nottinghamshire derby.
That meant Jaden Warner was handed a home debut in the back three alongside Kyle Cameron and Aden Baldwin, with Aidan Stone continuing in goal.
John Bostock partnered Scott Robertson once again in central midfield while, out wide, League Two’s January Player of the Month Jones joined Aaron Nemane in looking to supply an attacking trio of Crowley, David McGoldrick and Macaulay Langstaff.
We made a bright start to the game, Crowley seeing a shot blocked before minutes later working Nemane to the byline only for him to find the side-netting with his cross.
But, shortly after Stone had done well to race out of his area to snuff out a dangerous Jonny Williams ball on the counter, Crowley had us in front as the scampering Jones laid the ball off for him to finish brilliantly from 20 yards.
Crowley then had a good opportunity to set up our second as space opened up for him in the right-hand channel, with McGoldrick bursting into the area. Crowley’s cross had too much on it, though, and the ball ran behind.
The Gills warned us of their own threat as a deep cross from the right was met with no telling touch – but a similar ball proved our undoing moments later as Hawkins produced a firm header past Stone to level the contest on 20 minutes.
And the match was turned on its head 15 minutes later as, seconds after Robertson had sent a long-range effort wide, another cross from the right proved to be our downfall as the ball was guided home by the outside of Clark’s boot at the back post.
Half-time presented an opportunity to regroup and plot a way back into the game but, within eight minutes of the restart, the visitors had their third when Masterson was first to pounce as the ball was kept alive inside our area.
McGoldrick attempted to spark a response 10 minutes later as he tried his luck from range, only to send the ball well wide.
But chances were proving very hard to come by - and the scoreline could have got worse for us on 74 minutes as Stone failed to connect with a punch, before being able to make an important save with his feet to deny Gillingham on the follow-up.
With time ticking away, good work from Nemane resulted in a good chance for Langstaff in the area. With a defender in close proximity, he could only fire his low shot straight at Gills keeper Jake Turner.
We quickly created another chance as Jones stood a cross up for McGoldrick six yards out, but he couldn’t get enough power on his header to trouble the keeper.
And it wasn’t long before we were breathing a sigh of relief at the other end as Tim Dieng’s diving header hit both posts and stayed out, allowing us to turn the ball behind.
Six minutes were added on at the end of the match, with Langstaff sending a left-footed effort narrowly wide in the dying moments.
But there was to be no comeback as we suffered back-to-back defeats.
STARTING XI: Stone; Cameron, Baldwin, Warner; Jones, Nemane; Robertson (O'Brien 79'), Bostock (Austin 67'); Crowley, McGoldrick, Langstaff
SUBS: Ashby-Hammond, Rawlinson, Macari, Mahovo, Morias
BOOKINGS: Bostock 45+3', McGoldrick 88'