Second-half strikes from David Robertson, Noel Hunt and Willo Flood gave Dundee United a handsome victory at Love Street.
Dundee Utd's Prince Buaben and St Mirren's Billy Mehmet tussle for the ball
Robertson opened the scoring after a poor first half, rifling home from Barry Robson's cross to break the deadlock.
Hunt then scored from a Flood cross before St Mirren were reduced to 10 men with Hugh Murray sent off.
Flood then drilled a shot past Chris Smith and United held on for the win.
Buddies boss Gus MacPherson started with the same 11 that earned a point against Celtic at Parkhead last week. There were changes afoot for the visitors as Tannadice boss Craig Levein dropped off-form goalkeeper Grzegorz Szamotulski to the bench.
Youngster Euan McLean came in between the sticks in place of the Pole, as Mark Kerr and Jordan Robertson both dropped to the bench.
Dundee Utd started well, and Noel Hunt caused problems in the St Mirren defence with an early header from a Robson corner, however Billy Mehmet was able to clear.
Flood then passed up an opportunity for United, heading wide from only six yards.
St Mirren improved as the first half continued, with Mark Corcoran becoming influential in the attacking third and he sent a speculative effort narrowly over the bar.
United were profiting from cross balls, and Darren Dods perhaps should have done better when Chris Smith flapped at a Robson cross, but the defender put his header well over.
Hunt then had another chance, but his headed effort from around the penalty spot was comfortably over the bar.
The visitors took the lead after the break as in-form Robertson fired home a right-footed effort from Robson's cross.
St Mirren upped the tempo in a bid to grab an equaliser, and veteran Andy Millen tried his luck with a right-footed shot just inside the box, but United keeper Euan McLean was equal to the effort.
Ian Maxwell was next to try his luck, but his left-footed drive went wide of McLean's left-hand post.
It was Dundee Utd who claimed a second goal however, as Hunt slotted home from close range from a Flood free-kick.
The game then slipped away from St Mirren as they went down to 10 men after Hugh Murray saw a second yellow for a foul on Robson.
Things then went from bad to worse for the Buddies as Flood drilled a right-footed shot from the right side of penalty area past Chris Smith to seal the points for United.
St Mirren: Smith, van Zanten, Millen, Maxwell, Reid, Murray, McGinn (Kean 57), Mason, Miranda (Molloy 65), Corcoran, Mehmet. Subs Not Used: Howard, Potter, Burke, Brady, McCay.
Sent Off: Murray (81).
Dundee Utd: McLean, Dillon, Dods, Kenneth, Duff, Gomis, Flood, David Robertson (Kerr 80), Robson, Buaben, Hunt. Subs Not Used: Szamotulski, Conway, Cameron, Jordan Robertson, McCord, Don.
Goals: David Robertson 49, Hunt 77, Flood 90.
Ref: C Thomson (Scotland).