Three first-half goals gave Dundee United a mountain to climb as St Mirren picked up all three points at Tannadice.
A Joe Shaughnessy header and two hotly-contested Jamie McGrath penalties before the interval all but secured the Premiership spoils for the Buddies.
A long-range Ian Harkes strike on 54 minutes reduced the arrears for Micky Mellon’s men but Saints subs Dylan Connolly and Kristian Dennis sealed the deal for the away side.
The result means St Mirren move up to seventh, just two points behind the Terrors with three games in hand.
Deniz Mehmet replaced Benjamin Siegrist, struggling with a calf problem, between the sticks for United, while Luke Bolton and Marc McNulty came in for Lewis Neilson and Louis Appere.
St Mirren made three changes from Sunday’s Betfred Cup semi-final defeat to Livingston with Ryan Flynn, Ilkay Durmus and Jon Obika coming in for Cammy MacPherson, Connolly and Brandon Mason.
The Buddies started the brighter with Eamonn Brophy flashing an effort wide just a minute into the contest before proceedings settled down.
It was an even affair with the teams well-matched and both trying to get the ball down and play.
United’s front men showed what they were all about on 13 minutes as Bolton, Nicky Clark and Lawrence Shankland combined to good effect. However, the latter ran the ball out of play as he bore down on goal.
Richard Tait, who had a good one-on-one battle with Bolton all evening, saw an effort charged down by Mark Connolly before the Tangerines had their best chance of the first half.
Jak Alnwick had to get behind a Dillon Powers thunderbolt as he latched onto Connolly’s knock down inside the box. The rebound fell to the American but he blazed over.
Shankland fired wide on 25 minutes before Tait and Ethan Erhahon saw efforts blocked. Connolly nodded wide from a corner just before the half-hour mark.
The Terrors had claims for a penalty waved away shortly after that chance as Tait recovered to tackle Bolton inside the box, appearing to get the ball.
The visitors went up the other end a minute later and got the opener, much to United’s frustration.
Conor McCarthy latched onto a McGrath free-kick to nod a header across the box where he found defensive partner Shaughnessy in space, with the Irishman able to direct the ball back across Deniz for 1-0.
St Mirren were awarded a pair of penalties before the break and the opportunity to extend their lead.
On 41 minutes, Mark Reynolds was adjudged to have brought down Shaughnessy in the box and McGrath stepped up to send Deniz the wrong way to double the Saints’ advantage.
It was 3-0 to the Paisley men in first-half stoppage time. Shankland appeared to block a Flynn strike with his arm inside the area, allowing McGrath to once more lash home.
Harkes rocket pulls one back for United as Buddies run away with it
Moments into the second period, Shankland saw a volley comfortably caught by Alnwick.
Shaugnessy nodded over from a McGrath corner before United got themselves back in the match.
On 54 minutes, Harkes picked up a Bolton pass and unleashed a rocket from fully 25 yards for his first league goal of the season.
Buddies sub Dennis came close to restoring the three-goal lead for Jim Goodwin’s side but narrowly dragged his effort wide after good work from Durmus.
Connolly saw a header saved by Alnwick in the middle of the goal on 69 minutes as gaffer Mellon rolled the dice, bringing on Louis Appere as United chased the game.
Dylan Connolly came close on 76 minutes as the visitors continued to press for one more goal to kill the game as a contest.
And the rapid Irish winger found it on 80 minutes as he raced through on goal, dinking Deniz to make it 4-1.
It was five soon after as Dennis tapped home Flynn’s cutback as the visitors ran riot.
The Buddies saw out the rest of the match comfortably to head back down the road with a valuable victory.
Dundee United: Deniz (GK); Smith, Connolly, Reynolds (C), Robson; Bolton (Appere 72), Harkes, Powers (Fotheringham 45), McNulty; Clark, Shankland.
Subs not used: Siegrist (GK), Sporle, Pawlett, Edwards, Hoti, Mochrie, and Neilson.
St Mirren: Alnwick (GK); Fraser, McCarthy, Shaughnessy (C), Tait; McGrath, Flynn, Erhahon, Durmus (McAllister 81); Obika (Connolly 71), Brophy (Dennis 56).
Subs not used: Lyness (GK), Finlayson, Sheron, Henderson and Jamieson.
Referee: John Beaton.