Attendance 11,362
Manager Walter Smith made two changes from last Saturday with Kirk Broadfoot and Lee McCulloch replacing the injured Madjid Bougherra and DaMarcus Beasley against a side who have proved to be more than difficult opponents in recent years.
Rangers started brightly and snatched an early lead in ten minutes when Kris Boyd turned Mihael Kovacevic on the edge of the box to rifle home a Steven Whittaker cross that had been cleverly dummied by Steve Davis.
The visitors were well on top - five minutes later a Pedro Mendes header released Boyd through the centre of the United defence only for Paul Dixon to thwart him by turning the ball narrowly wide.
The game was being played almost entirely in the hosts' half - yet in a grim foretaste of what was to unfold in the second-half a Craig Conway corner in 28 minutes found Jon Daly rising unchallenged inside the six-yard box, his downward header being scrambled clear by Allan McGregor.
Rangers remained on top however - ten minutes later Lee Wilkie misjudged a lob back to his goalkeeper - and as Kenny Miller chased the loose ball it was the central defender who somehow got back to block his effort.
Referee Iain Brines, a surprise appointment to such a crucial game given that he is rated as the worst in the SPL, somehow managed to ignore a blatant body-check on Miller by Garry Kenneth as the Ranger raced through on a Mendes pass - but when the half-time whistle blew the only mystery for the 11,362 spectators was that Rangers were only one goal ahead.
The second 45 would be an entirely different story as Dundee United restarted on the ascendancy with Conway's corner being headed just wide by Daly in 47 minutes.
Two minutes later the scores were level when Paul Dixon raced down the left at pace, his cross to the far post being met by Lee Wilkie who scooped the ball into the net. It had been a first-class cross by the United full-back - but many onlookers questioned the inability of Allan McGregor to cut out either the original cross or Wilkie's shot that went back across his goal.
Rangers tried to respond immediately - Miller being bundled off the ball by Kovacevic as he moved onto a Boyd flick. To no-one's surprise however Iain Brines turned a blind eye.
Unbelievably despite their overwhelming first-half superiority the Ibrox men found themselves trailing in 53 minutes - and yet again it was a goal conceded from a cross ball with Warren Feeney heading home another Dixon cross. The ball should certainly have been cut out by McGregor, but the visitors central defence was also liable as was right-back Steven Whittaker who had failed to cut out either the left-back's run or cross.
Rangers had now fallen completely out of the game, and United threatened to add a third with both Dixon and Conway rampaging down the left, bypassing Whittaker as if he didn't exist - the high cross into the middle creating havoc and threatening a goal with every attack.
Walter Smith introduced both Kyle Lafferty and Nacho Novo in place of McCulloch and Miller in 62 and 68 minutes respectively, and right out of the blue the two substitutes combined in 75 minutes when a superb run by the Spaniard allowed the Ulsterman to slot the ball home for the equaliser.
The Light Blues were now back on top - and a shocking decision by linesman Gary Cheyne denied Novo in 82 minutes when he broke through on a Barry Ferguson pass only to be flagged offside when he was clearly on.
Rangers piled on the pressure in the closing minutes - Pedro Mendes stabbing just wide from Lafferty's pass in 86 minutes, then Ferguson's back-header from a Whittaker cross similarly missed the target.
Finally, in injury time, Whittaker's left-foot shot from twenty-yards skimmed the crossbar - and Rangers were left to rue the unnecessary loss of two points.
At the final whistle the referee was booed off the park, underlining his contribution to the result.
Afterwards Walter Smith reflected:
"We played well in the first-half and should have had the game won then. I was disappointed at the loss of the goals at the start of the second-half. We did well to get back into the game after falling behind."
DUNDEE UNITED Zaluska; Kovacevic, Wilkie, Kenneth, Dixon; Flood, S. Robertson, Gomis (Swanson 87), Conway; Feeney (D. Robertson 78), Daly
UNUSED SUBS McGovern, Dillon, Dods, O'Donovan, Shala
RANGERS McGregor; Whittaker, Weir, Broadfoot, Papac; Davis, Mendes, Ferguson, McCulloch (Lafferty 62); Boyd, Miller (Novo 68)
UNUSED SUBS Alexander, Beasley, Dailly, Aaron, Fleck
REFEREE iain Brines