McCoist travelled to Dumfries despite tendering his resignation hours earlier but saw goals either side of the break from Kevin Holt and Grant Reilly inflict a third defeat in five games.
The pressure on the Ibrox boss has intensified since last month’s 2-0 loss to Hearts and the Scottish Championship leaders could now pull 12 points clear on Saturday.
McCoist insisted he remained “committed” to the club when he spoke briefly before kick-off but he refused to answer questions about his next move after the final whistle.
A convincing performance on the pitch might have helped bring clarity off it but Rangers scarcely troubled hosts who now move to within four points of them.
John Baird and Iain Russell had fired warnings before the opener came, Holt finding the top corner with a fine free-kick in the 22nd minute after Darren McGregor was penalised for handball on the edge of his box.
Rangers had by then only mustered a lone Kenny Miller shot but they were briefly revived by the arrival of David Templeton for Dean Shiels.
Nicky Law’s curling effort was pushed away by Zander Clark and Miller should have struck on the rebound but
the resurgence was fleeting.
Lee McCulloch almost gifted Baird a Queens second with a weak headed clearance, the striker shooting narrowly wide.
But another McCulloch lapse saw the game settled with 23 minutes left, Reilly afforded time and space to lash in off the post after Daniel Carmichael spotted his run.
The ‘Super Ally’ chant briefly heard before kick-off from visiting fans was audible again – but this time from the gleeful home hordes.