Mark McKenzie's first goals for Ayr helped secure a stunning win at Dens Park tonight – and ignited David Hopkin's Somerset reign in style.
Another strike from Cammy Smith ensured United were on easy street during a thoroughly impressive display on Tayside.
Only a late consolation from Osman Sow could deny Ayr the perfect night but they sent out a huge statement of intent under their new gaffer.
Hopkin's men were hungry, well organised and more than deserving of a victory which, remarkably, propels them to within just three points of the promotion play-offs.
And it marks a giant leap of progress for the new boss less than a week into his new role.
Hopkin had rung the changes in just his second match with Ayr going for both a switch in personnel and formation.
Joe Chalmers, Michael Miller and McKenzie all came in for starts as United reverted to a 4-1-4-1 with Aaron Muirhead at the base of midfield.
Chalmers was asked to keep close tabs on Dens dangerman Paul McMullan down Ayr's left,while Miller and Luke McCowan played centrally with Cammy Smith on the right.
And from the off, Ayr looked bright and were the quicker to get to grips with the tricky Dens surface.
They had loud calls for a penalty turned down in the 11th minute when Miller was bundled in the box by Jordan Marshall, but referee Alan Newlands was not interested in the appeals.
At the other end, Viljami Sinisalo had to show quick reactions to deny Max Anderson from close range as the ball bounced dangerously around the Ayr box.
But on 18 minutes, United grabbed the breakthrough with a lightning counter attack which saw McCowan rob Paul McGowan before racing down the left and his centre was converted by the onrushing McKenzie for his first senior Ayr goal.
United took huge confidence from the goal and quickly began to dominate the middle of the park against an increasingly frustrated home side.
McCowan, in particular, was looking dangerous at every turn and he fired just wide after good setup work by Smith as they pushed for a second goal.
And he tried his luck again on the stroke of half time with an effort from distance which went just over the bar as Ayr continued to look the likelier when getting into the final third.
And they duly got their reward just minutes after the restart as the lead was doubled.
Superb work down the left from Paddy Reading saw the ball delivered into the box for McCowan and when his shot was blocked, Smith hammered home the rebound to put Ayr in charge.
Dundee boss James McPake threw on a raft of substitutes from the bench to try and turn the tide for the hosts but, Charlie Adam's dangerous deliveries aside, they rarely looked like breaching a well marshalled Ayr defence.
Sub Declan McDaid drew a good save from Sinisalo with a shot from distance, but it was Ayr who extended their lead with a goal right out of the top drawer.
McKenzie took possession 25 yards from goal and turned to rifle the ball into the top corner with all the confidence of a striker at the very top of his game.
Ayr were home and hosed but Sow managed to register a late goal for the Dark Blues as he clipped the ball over the advancing Sinisalo, but it could do nothing to take away from Ayr's night.
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