Gillingham 1 Carlisle United 0: Carlisle United's promotion push suffered an injury-time blow as Shaun Williams sent them to defeat at Priestfield.
The Blues were well below their best in a windswept contest at Priestfield - and then lost it at the death.
Home captain Williams ran onto a breaking ball in the box in the 93rd minute and rifled confidently past Tomas Holy.
There was no time for the Cumbrians to respond, and they fell out of the automatic promotion places as a result.
Paul Simpson's United looked set to cling onto third thanks to Stevenage's defeat to Salford City.
But the sting in the tale meant a first defeat in seven, leaving them winless in three and goalless in three as well as down to fourth.
Carlisle created little of note, with sub Kristian Dennis denied with a late chance.
Otherwise their display left much to be desired on their second of a three-game run of away fixtures.
Blues boss Simpson made three changes to the side that had started at Bradford on Tuesday.
That saw Joe Garner and Omari Patrick come back in along with John-Kymani Gordon, who got his first start since February 14.
They came in at the expense of Ryan Edmondson, Dennis and Alfie McCalmont.
Paul Huntington was still out with the abdominal injury that sidelined him in midweek, as Ben Barclay continued in defence.
For Gillingham there was on change, Aiden O'Brien taking Dom Jefferies' place.
A windswept first half of few chances then unfolded, Gillingham having the better of it without unduly worrying United's ex-Gills keeper Holy.
Barclay had to make a timely interception when the hosts looked to pick out Alex MacDonald from a corner.
Another set-piece then needed Holy to cut out a low delivery with his foot at the near post.
Carlisle, with the wind at their backs, struggled to make anything happen in their 3-4-3 shape, their best attempts defied by solid defending, a poor final ball and an inability to take any control of possession.
At the other end Simpson's defenders battled well against home frontmen Oli Hawkins and Tom Nichols when Harris's side fed the ball forward.
Only a couple of half-chances from the edge of the box registered as attempts, with MacDonald fizzing a 25-yarder over the bar in the 30 minutes.
Patrick then sliced an attempt wide from outside the Gillingham area as a hard-working but inspiration-light first half came to an end.
Before the second half even got under way there were bookings for Garner and MacDonald as they clashed at the restart.
The home side then looked to make the running as Nichols sliced a shot wide from the edge of the box, and then Hawkins headed over a MacDonald corner.
Simpson made a double change on 56 minutes, Edmondson and Jordan Gibson replacing Gordon and Garner.
Tim Dieng then failed to beat Holy with a volley after Nichols had got to the byline for the Gills.
United responded as Moxon fed Patrick, whose cross broke for the arriving Barclay, but a strong MacDonald challenge denied him, some Blues penalty appeals dismissed by ref Breakspear.
Home boss Harris then introduced George Lapslie and Jefferies, but United were making more of the running in this spell.
And after Simpson sent on Dennis and Jack Robinson, top scorer Dennis was sent towards the box to the right of goal, but home keeper Glenn Morris parried his right-footed finish.
Harris introduced ex-Carlisle striker Tristan Abrahams for the closing stages, before another former Blue, Max Ehmer, failed to beat Holy with a free header.
Moments later, Barclay brought down Abrahams and there were home calls for a red card, but ref Breakspear settled on a booking for the Carlisle defender.
Gillingham then finished the game the strongest - and their late pressure told as Williams pounced to sink the Blues.
Gillingham: Morris, Alexander, Masterson, Ehmer, McKenzie, Williams, Dieng, O’Brien (Jefferies 73), MacDonald (Lapslie 73), Nichols (Abrahams 83), Hawkins (Hawkins 90). Not used: Holtam, Tutonda, Coleman.
Goal: Williams 90.
Booked: MacDonald, Hawkins.
United: Holy, Barclay, Feeney, Mellish, Senior (Dennis 78), Armer, Guy, Moxon, Gordon (Edmondson 56), Patrick (Robinson 78), Garner (Gibson 56). Not used: Kelly, Whelan, McCalmont.
Booked: Garner, Moxon, Barclay, Feeney, Dennis.
Ref: Charles Breakspear.
Crowd: 6,110 (475 United fans).
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