Match ends, Inverness CT 4, St. Mirren 0.
Inverness Caledonian Thistle set up a Scottish Cup fifth round date with Partick Thistle after brushing St Mirren aside in this replay.
The sides drew 1-1 in Paisley but Caley dominated in the Highlands with Gary Warren nodding home the opener.
Greg Tansey made it 2-0 from the penalty spot after Jim Goodwin downed the excellent Marley Watkins.
Danny Williams added a third after the break and Graeme Shinnie made it 4-0 late on.
Inverness went into the game defending an unbeaten home record this season and before long they were bossing possession against a Saints outfit who looked every bit a team sitting second bottom of the Premiership.
John Hughes's charges hit the front through Warren's excellent near-post header from Tansey's delivery, but the visitors afforded the Caley man far too much space in the area.

Goodwin was back in the Buddies line-up following a three-match ban and, having given away the corner that led to the opener, his night got even worse as Caley doubled their lead minutes later.
The Irishman slipped after dithering on the ball in his own box and then downed Watkins to concede a penalty that Tansey fired home, sending Ridgers the wrong way.
With the visitors unable to contain their hosts now, Williams should have made it 3-0 after Watkins sent him clear, but his shot was easily saved by Ridgers.
St Mirren's goalkeeper then made another save from a James Vincent header but the Caley midfielder should have given the glove man no chance with what was a simple chance, following more fine play from Watkins.
The Paisley side made a better start to the second half and threatened to get back into the game, but their final ball was found wanting all too often.

And Inverness put the game to bed with a great break upfield.
Watkins ran from his own half and played a perfect pass infield for Billy McKay who blasted a shot off the bar, and when Sean Kelly fluffed his chance to clear it Williams was there to finish.
Warren then rattled the bar with an effort as the hosts looked like piling the pain on Tommy Craig's side.
Substitute Aaron Doran almost made it four with a dig from distance that dipped just over the bar.
Shinnie, however, did add even more gloss to the scoreline when the Buddies back line parted, allowing the full-back to help himself to a goal.
Line-ups
Inverness CT
Formation 4-4-1-1
- 12Brill
- 2Raven
- 6Meekings
- 5Warren
- 3ShinnieBooked at 3mins
- 4Vincent
- 8Draper
- 16Tansey
- 19WilliamsSubstituted forDoranat 76'minutes
- 15WatkinsSubstituted forChristieat 74'minutes
- 7MckaySubstituted forRossat 84'minutes
Substitutes
- 1Esson
- 10Doran
- 11Ross
- 14Devine
- 18Tremarco
- 20Polworth
- 22Christie
St Mirren
Formation 4-1-4-1
- 12Ridgers
- 2Naismith
- 4McAuslandSubstituted forBrownat 63'minutes
- 22Tesselaar
- 3Kelly
- 6GoodwinBooked at 22mins
- 14ReillySubstituted forDruryat 53'minutes
- 13OsbourneSubstituted forBallat 73'minutes
- 8McLean
- 7McGinn
- 9Thompson
Substitutes
- 10Marwood
- 16Ball
- 17Drury
- 19Brown
- 21Teale
- 28Kello
- 29Caldwell
- Referee:
- Calum Murray
- Attendance:
- 1,326
Match Stats
- Possession
- Home60%
- Away40%
- Shots
- Home19
- Away7
- Shots on Target
- Home9
- Away3
- Corners
- Home10
- Away2
- Fouls
- Home8
- Away11
Live Text
Post update
Full Time
Second Half ends, Inverness CT 4, St. Mirren 0.
Goal!
Goal! Inverness CT 4, St. Mirren 0. Graeme Shinnie (Inverness CT) left footed shot from the centre of the box to the bottom right corner. Assisted by James Vincent.
Post update
Attempt missed. Greg Tansey (Inverness CT) right footed shot from outside the box misses to the left.
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Corner, Inverness CT. Conceded by Jim Goodwin.
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Attempt blocked. Ryan Christie (Inverness CT) right footed shot from outside the box is blocked.
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Attempt missed. Aaron Doran (Inverness CT) right footed shot from outside the box is just a bit too high.
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Attempt missed. Steven Thompson (St. Mirren) header from the centre of the box is just a bit too high.
Substitution
Substitution, Inverness CT. Nick Ross replaces Billy McKay.
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Corner, Inverness CT. Conceded by Jason Naismith.
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Attempt saved. Aaron Doran (Inverness CT) right footed shot from outside the box is saved in the top centre of the goal.
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Sean Kelly (St. Mirren) wins a free kick in the defensive half.
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Foul by Greg Tansey (Inverness CT).
Substitution
Substitution, Inverness CT. Aaron Doran replaces Danny Williams.
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Attempt missed. Sean Kelly (St. Mirren) left footed shot from outside the box is too high.
Substitution
Substitution, Inverness CT. Ryan Christie replaces Marley Watkins.
Substitution
Substitution, St. Mirren. Callum Ball replaces Isaac Osbourne.
Post update
Attempt missed. Gary Warren (Inverness CT) right footed shot from the centre of the box is too high.
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Gary Warren (Inverness CT) hits the bar with a header from the centre of the box.
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Corner, Inverness CT. Conceded by Jim Goodwin.