Caolan Boyd-Munce
Owen Oseni slides fellow substitute Caolan Boyd-Munce through on goal, and the Northern Irishman fires a lovely left-footed shot into the top corner to make sure of St Mirren's place in the next round.
Queens have made it difficult for the Premiership side, but that will do it.
Aberdeen end a run of 12 games without a victory as they survived an early scare to ease past Elgin.
The fourth-tier hosts gave the Dons some early frights, but the Premiership dominated after Shayden Morris' 21st-minute opener.
And they were left angered by the visitors' second, claiming that the first of Duk's second-half double had not crossed the line before ending the game with 10 men.
Image source, SNSA brace from Martin Boyle either side of Rudi Molotnikov's close-range strike earns Hibernian their place in the fifth round of the Scottish Cup.
It was an extremely comfortable afternoon for the home team against sixth-tier Clydebank, who receive a warm reception from their huge travelling support.
Image source, SNSGoals from Boyle and Molotnikov seal Hibs' passage into the fifth round
A much-needed boost for Simo Valakari's St Johnstone, who have been struggling in recent weeks.
Despite being bottom of the Scottish Premiership, they've booked their spot in the fifth round of the Scottish Cup.
It's more bad news for Stuart Kettlewell's side who, after a League Cup semi-final at Hampden earlier this season, crash out of the Scottish Cup at their first hurdle.
Image source, SNSJay Henderson (hat-trick)
The goals keep coming for the Honest Men.
Watch: Henderson scores his hat-trick
Ross County 2-2 Livingston
That's the end of the 90 minutes at the Global Energy Stadium, and we're heading to extra-time.
Livingston have had the better of the chances, but the teams cannot be split.
Zak Rudden
It looks like we'll get extra-time at the national stadium.
Hibernian 3-0 Clydebank
Lewis Miller and Junior Hoilett force Bankies keeper Andrew Leishman into two strong saves in quick succession.
Miller first tests Leishman with a powerful drive, before a smothering stop was enough to keep out Hoilett's placed effort.
Duk
Duk grabs his second moments after being denied by a goalline clearance.
The winger curls a drive off the far post.
Watch: Duk scores Dons' third
Ross County 2-2 Livingston
Robbie Muirhead shoves Zac Ashworth over on the touchline, then boots the ball off the County sub.
Everyone's involved now, right in front off the dug-outs. Nohan Kenneh and Cristian Montano have to be separated.
Yellow card for Muirhead after all that.
Queen of the South 1-2 St Mirren
The Doonhamers are throwing everything at St Mirren in search of an equaliser, but the visiting defence have had the answers so far.
Elgin City 0-2 Aberdeen
Ten-man Elgin have a chance to get themselves back in the game.
Olly McDonald is through on goal, but the sub striker's shot is straight at goalkeeper Ross Doohan.
However, the Dons are quickly up the other end and force a good save from Aidan Glavin.
Sean McGinty
The Championship side strike late. Will that be enough to avoid extra-time?
Watch: McGinty's late strike for Accies
Elgin City 0-2 Aberdeen
Willie Miller
Former Aberdeen captain on BBC Sportsound
It's been a good performance from Aberdeen. This could have been a slippery one for them.
Dylan Watret
Ouch! A proper hiding.
Watch: Watret makes it seven
Myles Gaffney
Watch: Gaffney doubles Cove's lead
Ben Wilson
Elgin City 0-2 Aberdeen
No way back for the fourth-tier hosts now as defender Lyall Booth is shown a second yellow card.
Brennan Dickenson
Hope for the hosts, who fight to keep the ball alive in the St Mirren box, before Brennan Dickenson fires a left-footed volley into the bottom corner.
It's a wonderful strike and sets up a grandstand finish at Palmerston.
Watch: Dickenson pulls one back for the home side
Chris Mochrie
Highlights: Hamilton Academical 3-1 Musselburgh Athletic
Manager: John Rankin
Formation: 4 - 2 - 3 - 1
Manager: Liam Burns
Formation: 3 - 5 - 2
Manager: John Rankin
Formation: 4 - 2 - 3 - 1
Manager: Liam Burns
Formation: 3 - 5 - 2
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