Barnet boss Mark Stimson was unable to see off his old club at Underhill this evening.
Instead, it was ex-Bees Andy Hessenthaler and Ian Hendon, now boss and assistant respectively at Gillingham, who were celebrating at the final whistle.
But at half-time it did not look like the visitors would come away with the spoils.
Barnet led through a Kevin Gallen goal, his first for the club, and looked to be heading for a second consecutive win.
However, the Gills turned it round with two goals in five second-half minutes.
Bees boss Stimson named the same side that saw off Northampton so convincingly at the weekend.
Though Gillingham saw lots of the ball and created plenty of chances in the first half, it was the hosts who struck on the half-hour, Gallen scoring from close range after good work by Mark Marshall.
But it all went wrong on the hour, Chris Whelpdale grabbing an equaliser, before Charlie Lee hit a second just five minutes later.
Stimson threw on strikers Izale McLeod, Ricky Holmes and Mauro Vilhete in a bid to salvage a point, but the Bees could not grab an equaliser.
Incredibly, after going all last season and this current one without an away win, Gillingham have now won twice on their travels in the space of three days, having finally ended the barren spell at Oxford United on Saturday.
For the Bees, after the euphoria of the weekend's win over the Cobblers, it is back to the drawing board, and they remain in the League Two relegation zone.
BARNET (4-4-2): Cole; Devera; Basey, Uddin, Parkes; Francomb, Southam, Hughes (Holmes 76 (Vilhete 85)), Marshall; Gallen (McLeod 66), Kabba. Subs not used: Coulton (GK), Cox, Jarvis, C Stimson.
Attendance: 2,519.
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