Billy Sharp and Kieron Freeman scored either side of the break for Chris Wilder's side who, it emerged before kick-off, have lodged a bid for Bradford City centre-forward James Hanson.
But the visitors claimed a share of the spoils thanks, in no small part, to the heroics of Stuart Nelson. United will be disappointed by their failure to prevent Josh Wright netting his first goals since October. But, given the welter of openings they engineered throughout this match, Nelson was ultimately responsible for denying them victory.
Sharp has added a different dynamic to his game since being appointed captain following Wilder's appointment in May. But his greatest strength is still scoring goals. With Gillingham packing their defence whenever United had the ball, the first-half shot which broke the deadlock midway through the first-half should have been the turning point of the game.
Instead, with Stuart Nelson excelling himself between the posts, Gillingham clawed themselves back on level terms early in the second and dragged United back into the arm-wrestle before taking a shock lead. Wright, who had earlier taken advantage of a defensive lapse to equalise, claimed his second of the afternoon when United's backline failed to deal with Ryan Jackson's long- throw.
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Wilder has made no secret of the fact his team must overcome "bumps in the road" between now and the end of the campaign. Staring at the possibility of a second successive league defeat, United demonstrated great conviction by dusting themselves down and carving the opportunity which saw Freeman smash home.
But with the opposition keeping their shape and tactical discipline under pressure, they were unable for force a winner and extend theiir advantage over both Scunthorpe and Bolton Wanderers whose fixtures were both postponed.
Wilder had conceded Gillingham could catch his team unawares following Adrian Pennock's appointment as head coach earlier this month. But the game began in familiar fashion with United looking to stamp their authority on opponents who put nine men behind the ball whenever they lost possession. Despite the inevitable lack of space, Jack O'Connell still found enough room on the by-line to whip a low fifth minute cross into the penalty box which Matt Done, unaware he had been flagged offside, nearly swept home.
After a slow start to his career in South Yorkshire, John Fleck has blossomed into the division's most creative force of late. The former Scotland under-21 international embellished his reputation by delivering a delightful centre into Nelson's area moments after testing the goalkeeper with an effort from range. Sharp, ghosting in front of his marker, read the trajectory of the ball perfectly but misjudged his angles and headed over the crossbar.
Gillingham, despite failing to reproduce the form which saw them challenge for the play-offs last season, still have plenty of talented players at their disposal. One of those, teenager Elliott List, dragged wide on the counter attack midway through the opening period. But Sharp made no mistake in the 32nd minute when he fired home past the onrushing Nelson.
Justifying Pennock's decision to select him ahead of new arrival Tomas Holy, Nelson twice foiled Sharp in quick succession before Wright pounced early in the second-half. He was on target again in the 58th minute following another defensive lapse. But, showing their mettle, United restored parity when Freeman thrashed the ball into the roof of the net after Caolan Lavery had forced a save.
Sheffield United: Moore, Fleck, O'Connell, Basham, Lavery (McNulty 72), Sharp, Done (Scougall 80), Coutts, Freeman, Ebanks-Landell, Duffy. Not used: Ramsdale, Jake Wright, Riley, Wilson, Reed.
Gillingham: Nelson, Jackson, Herd (Osadebe 46), Ehmer, Oshilaja, Wagstaff, Hessenthaler (Byrne 84), McDonald, List (Donnelly 57), Dack, Josh Wright. Not used: Knott, Hadler, Dickenson, Emmanuel-Thomas.
Referee: Ben Toner (Lancashire). Attendance: 20,649.