Billy Dodds had fired the home side in front in only the first minute, but there seemed no way back for Ian McCall's side when they went in at the break 3-1 down.
Steven Thompson fired two quick replies, including one from the penalty spot, and substitute Hamed Namouchi, who had come on for injury-victim Gavin Rae, gave his side a substantial cushion just before the break.
But United were not to be denied and deserved a share of the spoils in an unexpectedly entertaining and feisty end-of-season encounter.
There was frantic activity on the pitch from the very first kick and United opening the scoring after just 40 seconds. Dodds was the scorer from close range position after Mark Wilson had fired in a free-kick to where he was lurking at the back post.
Rangers replied with a brace of goals from Thompson, his first double for the club he joined from United last season.
The first was an excellent, sixth-minute response to barracking from the fans who used to cheer him when he arrived in the box ahead of his market to convert a Chris Burke cross from the right.
Thompson was booked by erratic match official Dougie McDonald for over-vigorous celebrations and was more circumspect when he made it 2-1 in the 14th minute from the penalty spot after Stephen Hughes had been fouled by David McCracken.
French-Tunisian Namouchi replaced Michael Mols in the first period and put his side 3-1 up just before the break. Frank de Boer sent a free-kick downfield and when the flag stayed down Namouchi beat Gallacher at the second attempt after the goalkeeper had parried his initial effort.
United took McInnes off at the break to increase their attacking options by sending on striker Scotland.
Rangers made a change themselves in the 53rd minute but it was one they wished they could have avoided when Rae, who had just made a fine run into the box that needed Alan Archibald's intervention, was stretchered off.
Scotland was the centre of attention six minutes later when he fired his side back into the game.
Andy McLaren had got the better of Ball down the right and when the Trinidad international had taken his headed pass down on his chest he had little difficulty striding away and firing past Allan McGregor.
Scotland made Rangers pay in stoppage time by thumping home a loose ball in the box after Frank de Boer had been unable to clear while under pressure from Robson.
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