The 36-year-old, who played for the Millers seven seasons ago, latched onto Danny Kedwell's flick from a long Chris Whelpdale throw for the sole strike in the 22nd minute at Priestfield. Gillingham now sit 11 points clear of fourth-placed Cheltenham and 12 ahead of Burton, who are fifth and have one game in hand like Port Vale in second and Northampton in third.
Steve Elliott's goal late in the first half kept Cheltenham's hopes of a top-three finish alive at they beat automatic promotion rivals Northampton 1-0 at the Abbey Business Stadium.
Keanu Marsh-Brown struck five minutes from time on his Barnet debut to ease their relegation fears and hand AFC Wimbledon a 1-0 defeat. The Dons dominated much of the game but could not find a way through, Chris Hussey's disallowed goal with 15 minutes to go the closest they came.
Jeff Goulding came off the bench to score the winner for bottom-of-the-table Aldershot as the League Two strugglers moved to within two points of safety with a last-gasp 3-2 win over Oxford.
James Beattie scored an injury-time equaliser to boost Accrington's battle against relegation in an exciting 3-3 draw with promotion-chasing Burton.
Returning hero Richard Cresswell helped York end a 16-game winless run with a 2-0 victory over Plymouth which keeps alive their Football League survival hopes.
Bradford maintained their slim play-off hopes with a 3-1 comeback win at relegation-haunted Torquay.
Tom Pope rescued promotion-chasing Port Vale again with a late header after former Valiants striker Marc Richards scored twice for Chesterfield in a 2-2 draw at the Proact Stadium.
French striker Oumare Tounkara made a big impact on his first start for Bristol Rovers as he scored twice in a 4-2 victory at Dagenham. The former Sunderland man, who arrived on a short-term deal at the end of February, helped John Ward's side to a fourth game without defeat.
Wycombe produced the 1-0 victory they needed to virtually secure safety in a forgettable match at Macclesfield. Stuart Lewis was the man who sparked the vital win for Gareth Ainsworth's side as he lashed home a shot from 12 yards out in the 55th minute after the Morecambe defence had failed to clear their lines after Matt Spring's deep free-kick was headed into the danger area.
Rochdale threw a spanner in the works of Exeter's promotion hopes with two late goals in a 2-1 win at St James' Park.
Barry Corr's late header salvaged Southend a 1-1 draw against Fleetwood in boss Phil Brown's first home game in charge of the club.