St Mirren scored the only goal of a pacy match against Dundee United at Tannadice to progress to the last eight of the Scottish Cup.
Following a dry first-half, Andy Dorman opened the scoring shortly after the break with a close-range shot.
United's Noel Hunt could have levelled matters with a spectacular overhead kick, but Mark Howard saved superbly.
Gus MacPherson's side held out until the final whistle and now face a quarter-final tie against St Johnstone.
Craig Levein was forced to make three changes to the United side that drew with Hibs on Saturday, with Christian Kalvenes, David Robertson and Mark de Vries all given starts.
St Mirren were without Chris Smith due to illness, with Mark Howard making his St Mirren debut in goal.
The controversy before the match may have centred on St Mirren's complaints about referee Alan Freeland, but the Buddies opted to focus on the task at hand.
In the first 10 seconds, Mark Corcoran sent in a low cross for Craig Dargo, only for Kalvenes to prevent a goal-bound effort.
St Mirren could have taken the lead after 16 minutes when United keeper Lukasz Zaluska blundered with the ball on the touchline and Dargo pounced, only to send his effort across the face of United's empty goal.
As the half-time whistle approached, chances to open the scoring were even between the sides, and the final opportunity of the opening 45 minutes fell to United's Craig Conway, but his low shot was held well by debutant Howard.
Just three minutes after the re-start, St Mirren opened their account when Dorman delivered in a delightful right-footed effort from the middle of the penalty area after Dargo had nodded down.
Four minutes later, Noel Hunt could have quickly levelled the scores, but watched as his close-range header sailed over the bar.
In the 62nd minute, Hunt sent in a right-footed shot from the edge of the penalty area, but Howard made a confident save.
Howard remained unthreatened for long periods in the last 20 minutes of the match, as United struggled to even the score.
But despite some good work by Willo Flood in the latter stages of the match, the Buddies remained in charge.
The tempo of the tie increased in the final 15 minutes, and Hunt added to the atmosphere when he sent in an acrobatic overhead kick with 13 minutes remaining after De Vries flicked on, but Howard pulled off a spectacular save to tip the effort over the bar.
As the final whistle neared, United appeared to run out of steam and failed to demonstrate the determination displayed by St Mirren and the Buddies made their way in to the quarter-finals of the Scottish Cup against St Johnstone.
Dundee Utd: Zaluska, Flood, Wilkie (Dillon 82), Dods, Kalvenes (Odhiambo 88), Kerr, David Robertson (Swanson 57), Gomis, Conway, Hunt, De Vries. Subs Not Used: McLean, Buaben.
Booked: Wilkie.
St Mirren: Howard, Barron, Potter, Haining, Maxwell, van Zanten, Murray, Dorman, Corcoran, Mehmet, Dargo (Kean 82). Subs Not Used: Mathers, Miranda, McGinn, Millen.
Booked: Mehmet, Dargo.
Goals: Dorman 48.
Att: 3,723
Ref: A Freeland (Scotland).
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