Last season’s Scottish Cup finalists marched into the fifth round of the competition thanks to a thrilling 2-1 win over Motherwell at Fir Park.
The Tangerines fell behind to a Henrik Ojamaa goal after just seven minutes and suffered a fairly miserable first half.
Transformed after the break, though, they wore down Well with wave after wave of attacking football.
They equalised with a bullet header from John Souttar then grabbed the lead with just eight minutes to go when Keith Watson nodded home.
The result was all the more praiseworthy because of their selection problems.
Manager Jackie McNamara’s plans were disrupted just minutes before the start when Jaroslaw Fojut called off injured in the warm-up and was replaced by Watson.
That meant Sean Dillon switching into the centre alongside Souttar, with Watson slotting in at right-back.
It was the last thing the Tangerines needed, with the club already minus suspended duo Nadir Ciftci and Callum Morris, as well as injured pair John Rankin and Mario Bilate.
What United did have was a 2000-plus away support, which gave them brilliant backing from the opening whistle.
The visitors’ first chance arrived on five minutes when Gary Mackay-Steven ran the ball to the byline before cutting back into the six-yard box but keeper Dan Twardzik did well to intercept before the cross reached Ryan Dow.
However, they were a goal behind after just a couple of minutes later when Ojamaa fired a low shot from outside the box past United goalie Rado Cierzniak and into the net to make it 1-0 to the hosts.
A sweeping move on eight minutes involving Stuart Armstrong and Chris Erskine saw Mackay-Steven picked out with a slide-rule pass but Twardzik did well to block the shot.
United’s Paul Paton was unlucky to be booked for reacting to a late challenge from Well’s Iain Vigurs, with the home player correctly cautioned for the foul.
The Tangerines were oh so close to levelling on 26 minutes after Mackay-Steven sprung forward. He was tackled but the ball broke to Armstrong at the edge of the box. The midfielder played a one-two with Erskine and when he got the ball back he slid it across the face of goal and just past the far post.
United once again came within a whisker of scoring when Dow found himself right in front of goal but his shot was saved by Twardzik.
Erskine then tried his luck as United piled on the pressure but his strike from the edge of the area was deflected for a corner.
Conor Townsend was booked for a tackle on Well’s John Sutton before the half came to a conclusion.
United brought on Calum Butcher for Charlie Telfer to add some much-needed muscle in the middle of the park.
A neat passing move from the visitors just a minute into the second period ended with Erskine blasting over from the edge of the box.
There was a blow for the hosts just a minute later when Paul Lawson limped off to be replaced by Craig Reid.
With more steel added to the core of the midfield, the Tangerines seemed better balanced and they had their fans on their feet on 51 minutes.
It was Erskine again who latched on to the ball and his 20-yard and shot was netbound until Twardzik dived to push the ball away.
United continued to pin the Steelmen back and, on 58 minutes, Twardzik was the home hero again when he came out to block a Mackay-Steven shot from point-blank range.
That was the Tannadice winger’s last contribution as he was replaced by Aidan Connolly on 61 minutes.
Finally, after so much hard work, United pulled themselves level on 66 minutes.
It was young Souttar who was the hero, leaping to head into the net from an Armstrong corner.
With their large support roaring them on, the visitors should have been 2-1 just two minutes later when but Butcher blasted his shot straight at Twardzik.
Then, on 70 minutes, the other sub cut in from right and blasted a shot just over the Steelmen’s bar.
It was all United now and some Connolly bobbing and weaving out right created space for a cutback to Dow, whose vicious strike was once again saved by the excellent Twardzik.
They wasted another glorious chance on 80 minutes, though, when Connolly sent Armstrong clean through. With only the goalie to beat Armstrong tried to take it around Twardzik only for the big man to grab the ball from his feet.
However, they got the goal their pressure deserved on 82 minutes thanks to the unlikely figure of full-back Watson.
It was a great ball in from the left by Townsend and the defender rose high to rocket a header down and past Twardzik to make it 2-1.
Sutton missed with a header from close range for the Steelmen in stoppage-time but it was to be United’s day.