Derek Stillie was the hero for Dunfermline with a truly outstanding performance as the Pars stole the points in injury time at Tannadice.
After completing a similar fete across the road at Dens last week, the Fife side withheld all the Tangerine pressure to sneak the points.
The hosts began in determined fashion claiming a penalty in the sixth minute when Stillie upended Jim McIntyre as the striker tried to round him.
Mark Wilson converted the spot kick but the lead only lasted 60 seconds as United reciprocated the gift.
Ex-Tannadice favourite Craig Brewster, yet again the visitor's most outstanding outfield player, fed the ball out to the unmarked Richie Byrne.
His curling cross was watched by three United players allowing Andy Tod the chance to bundle the ball in from only three yards.
The game continued to swing from end to end. United were frustrated again when a left-foot driven shot by Jason Scotland on the half-hour mark looked at certain goal but Stillie somehow stopped it with his inside heel.
While at the other end, Darren Young had an ideal opportunity to put his team ahead five minutes from the break when United's static defence gave him space with only the keeper to beat but he slid the ball wide.
But it was United who came closest to the breakthrough just before the break with only a miracle stop from Stillie preventing the goal.
McIntyre superbly created space for himself before curling a shot into the top corner. The keeper threw himself to tip the ball onto the bar and over.
The Tangerines' second-half response was expected. They pushed forward in numbers. A superb move by Grant Brebner and the impressive Karim Kerkar ended with McIntyre narrowly missing.
Then minutes later, Scotland forced himself across the box before cracking a bullet off the face of the bar.
Not to be outdone, the referee added some controversy into the match when he denied United a second penalty in the 58th minute when Andrius Skerla clearly pulled the shirt of McIntyre.
Ten minutes later man-of the match Stillie yet again pulled off a tremendous save from Scotland to complete a wonderful display.
Then came a diving headed goal from Young as Billy Mehmet broke away to leave United rock bottom.