SAINTS plummeted to the bottom of the SPL as they suffered their fifth successive loss on a disappointing afternoon at Love Street.
Irishman Jon Daly did the damage with a goal in either half, while the wasteful Buddies were made to pay for failing to take a host of gilt-edged chances.
Andy Dorman, Dennis Wyness and Billy Mehmet all failed to take glaring opportunities.
Meanwhile Stephen McGinn rattled the crossbar in the second half.
There was little to choose between the sides but the Tannadice men headed back to Tayside with the points thanks to hitman Daly.
Meanwhile Richard Offiong’s winner for Hamilton against Kilmarnock lifted the New Douglas Park outfit above Saints to send the Paisley men to the foot of the table.
Buddies boss Gus MacPherson made just one change from the side that was beaten 3-1 by Celtic last Saturday.
Will Haining dropped out through injury and Scott Cuthbert slotted in alongside skipper John Potter in the centre of defence, while midfield maestro Gary Mason again missed out.
The visitors were quick out of the traps and had Saints on the ropes inside 60 seconds when Willo Flood sent over an inviting cross which Francesco Sandaza fired across the face of goal.
Then Morgaro Gomis found space on the left and picked out Sandaza, but the Spaniard’s effort was too close to Love Street number one Mark Howard.
Sandaza had another chance a minute later when he ghosted into the six yard box to meet another Gomis cross but he couldn’t keep his effort down.
The home side were under the cosh at this stage but they almost opened the scoring at the other end in the fifth minute when Dorman’s first time shot deflected off Wyness on the six yard line. Unfortunately for the hosts the ball looped on to the roof of the net.
Dorman had another chance in 11 minutes when Craig Dargo and McGinn combined well with the former setting up Dorman 20 yards out, but with bags of time the former New England Revolution ace fired well over.
Then United had another chance to break the deadlock when Cuthbert fouled Danny Swanson on the edge of the box. But Paul Dixon sent his free-kick straight into the wall before Swanson fired over.
Arabs wideman Gomis was causing Jack Ross problems on the right channel and he went by the Saints full-back in the 15th minute and dangerously cut inside. But his shot was straight at Howard in the home goal.
The game was flowing from end to end as both teams strived to find an opener and McGinn created an opening for himself in the 26th minute when he cut in from the left after a good run, but he couldn’t keep his effort down.
Saints should have had a free-kick in a dangerous area a minute later when Franco Miranda’s cross from the left struck the arm of Flood just outside the box, but ref Calum Murray waved away the Argentinian’s claims.
On the half hour Craig Levein’s men threatened again with the industrious Swanson trying his luck from 25 yards, but his shot was just too high.
Then at the other end Dorman should have broken the deadlock when Wyness sent him one-on-one with the keeper with a great through ball.
But just as the Welshman was about to pull the trigger Michael Kovacevic got back to make a fantastic saving tackle and knock the ball behind for a corner.
And how Saints were made to pay. Less than 60 seconds later Flood had found space on the right and sent over a teasing cross to the six-yard line where Daly was waiting. The Irishman stooped to bullet a header past Howard. The Buddies keeper got a touch to the ball but there was too much power on it to keep it out and United had the breakthrough.
The visitors were again the first to try their luck in the second period with Swanson and Sandaza both chancing their arms in the early stages.
But in the 52nd minute the Love Street faithful were stunned into silence when Wyness missed an absolute sitter.
Miranda fed Garry Brady and he sent a great ball across the face of goal to the unmarked striker, but as the crowd waited for the net to bulge the former Inverness man got his angles all wrong and sent the ball high and wide.
It was a truly embarrassing miss and not even the offside flag of the stand side linesman could spare Wyness’ blushes.
Then troublesome Spaniard Sandaza found space in the home box but Miranda was on hand to curtail his advances.
Dorman then had another great opportunity to haul Saints level when he burst forward from the middle of the park into the box, but again just as he was set to shoot Garry Kenneth got across to produce a magnificent block to thwart the danger.
That prompted Love Street gaffer MacPherson to shuffle his pack and he hooked Wyness and Brady for Jim Hamilton and Steven Robb, with the latter moving to left-back and Miranda moving to the left of the midfield four.
But the game drifted into a lull as both sides conceded possession cheaply, and with 19 minutes remaining MacPherson made his final change with Dorman coming off for Mehmet with the big Englishman playing as an attacking midfielder.
United also made a change with Craig Conway replacing Sandaza and the sub quickly made his presence felt when he put in a great cross from the left for the diving Flood, but his header was just off target, while Scott Robertson went close with a chip moments later.
Then with 14 minutes remaining there was a real flashpoint in the Arabs box when goalkeeper Lukasz Zaluska reacted furiously to a late tackle from Hamilton.
As the pair went head to head the Pole appeared to headbutt the Saints striker who went down like a ton of bricks.
Whether there was sufficient contact to merit Hamilton’s reaction is debatable but whistler Murray clearly didn’t think so and instead flashed a yellow card at both players.
Daly then almost got his second of the game 10 minutes from time but his sizzling volley from the edge of the box was brilliantly beaten away by Howard.
Then Saints tried their luck and Mehmet advanced down the left with a great surging run and as he hit the byline he looked up to see Dargo pulling off his marker. But as he tried to pick out the striker with a cut-back Kenneth got back to make a block.
McGinn then went agonisingly close to levelling within seconds, then Mehmet headed the ball into his path but from the angle of the box the youngster’s ferocious volley was magnificently touched on to the bar by the fingertips of Zaluska.
The Buddies were really pushing for an equaliser and Mehmet had a good chance with five minutes left when Hamilton put it on a plate for him six yards out, but he sent his header well over.
Then Dargo fired over from 12 yards after good work by McGinn as Lee Wilkie hovered over the pint-sized hitman. But in the final minute United put the game to bed when Ross clumsily brought down Conway after the sub had sold him a dummy. Daly drilled home the resultant spot-kick to complete a miserable afternoon.