Cheltenham Town slipped to a third consective defeat after a disappointing display at the Abbey Business Stadium.
Boss Mark Yates apologised to the supporters after the game, describing the performance against Gillingham as his side's worst of the season.
They were simply below their best at both ends of the pitch on a soggy afternoon in Gloucestershire.
All the damage was done in eight minutes either side of the break, Cheltenham paying the price for some catastrophic defending which allowed the Gills to open up a two-goal lead.
Winger Jordan Obita was the grateful recipient, grabbing the goals to punish Cheltenham's profligacy in front of goal.
Chris Whelpdale added the third seven mintues from time to consign Yates' side to their fifth home defeat of the campaign.
The Kent side began the day in eighth, ten points adrift of the Robins but the result further conjests the promotion picture at the top of League Two.
Ten games to go then, but Cheltenham remain in the thick of it despite this result as the finishing line draws near.
Certainly tough games loom, but the management and players need the supporters' backing now more than ever.
When was the last time Cheltenham Town did anything the easy way?
Left back Luke Garbutt returned to the side after sitting out the 1-0 defeat by the league leaders at the County Ground.
Keith Lowe made way for the Everton loanee, otherwise boss Mark Yates kept faith with the side which performed so well without reward last weekend.
Sido Jombati returned to right back for this one, with Yates sending out his team in the 4-5-1 system which has served them so well this season.
Gillingham, depleted of several players through injury and suspension, made three changes of their own.
Defeat by Crewe Alexandra last weekend ended a run of four consecutive wins which had moved them within a point of Oxford United in the final play-off berth.
They too shaped up in a 4-5-1 formation and set out to frustrate the home side in the opening exchanges with a well-organised defensive line.
Darryl Duffy drew the first save of the game as early as the third minute following a neat passage of play culminating in a low shot by the Scot.
However Argentine goalkeeper Paolo Gazzaniga dropped low to hold the effort from the edge of the box.
Russ Penn was presented with a great chance to test the former Valencia shotstopper with 18 minutes on the clock, but the midfielder fluffed his lines after McGlashan had found him with a low ball from the right.
Luke Summerfield breathed a sigh of relief two minutes later when his mistake allowed Oliver Lee an opening from 20 yards, but midfielder failed to find the target.
Cheltenham went close ten minutes before the break when Penn rolled one into the path of Duffy, who poked it under Gazzaniga only to be denied by a Danny Jackman clearance.
There was controversy when Kaid Mohamed was unceremoniously dumped to the ground by Simon King 40 yards from goal.
The home support had felt the infringement merited stronger action by referee, but Mr. Madley cautioned the centre half for the offence.
In any case the assistant referee had flagged for offside so play was restarted by the visitors, who shortly afterwards went close when Lee fired narrowly wide from 25 yards.
The warning signs were there again when Dennis Oli skewed a volley wide with half-time approaching.
But it was Obita who handed his side the lead, taking full advantage of Jombati's hesitancy in the final minute of the half.
The England youth international ran onto Lee's through ball, wrestling it free from the right back before stabbing home past Jack Butland to put an entirely different complextion on Yates' half-time briefing.
Things went from bad to worse eight minutes after the restart when the former Reading winger doubled the advantage, profiting from some more dubious defending to bag his second of the afternoon.
Cheltenham set about getting themselves back into the contest, and Alan Bennett had met a Garbutt corner at the far post to draw a smart save from Gazzaniga.
But when the Gills number one pumped it downfield, the skipper misread the ball and allowed it to bounce, allowing Obita to nip in and lift the ball over Butland.
Oli then went past Garbutt too easily to graze the crossbar with an angled effort before Yates took action, making a double switch.
Marlon Pack had been booked for dissent when he was withdrawn by Yates, replaced by Jimmy Spencer while Josh Low was sent on in place of Mohamed.
The manager switched to a 4-4-2 formation, pairing Low and Summerfield in the middle and using low on the left.
Spencer joined Duffy in attack, but it was Jombati with the next chance, heading wide Garbutt's delivery on the hour.
The 382 supporters who had travelled over from Kent felt their side should have been awarded a penalty when substitute Jo Kuffour went to ground with 20 minutes remaining, but referee Mr. Madley waved away their claims.
Next Gillingham top scorer Danny Kedwell saw his first effort of the afternoon blocked by Butland five minutes later.
Jeff Goulding was then pressed into action, taking Garbutt's place who was clearly unhappy with the manager's decision to substitute the left back.
The heavens opened above the Abbey Business Stadium as the game drew to a close, and with Cheltenham chasing the game they became more even more exposed at the back.
And with seven minutes remaining Whelpdale struck, capping a miserable afternoon for the home supporters by converting Danny Kedwell's low ball across the box to make it three and secure a comfortable victory for his side.
CHELTENHAM TOWN: Butland; Jombati, Elliott, Bennett (c), Garbutt (Goulding 76); McGlashan, Summerfield, Pack (Spencer 57), Penn, Mohamed (Low 57); Duffy. Subs not used: Lowe, Smikle.
GILLINGHAM: Gazzaniga; Fish, Essam, King, Jackman; Oli (Kuffour 61), Lee, Whelpdale, Payne, Obita; Kedwell (c). Subs not used: Frampton, Evans, Hawkes (Gk), Miller.
REFEREE: Andrew Madley
ATTENDANCE: 3,137 (382 from Gillingham)