Airdrie turned on the style to thump Montrose as they closed in on League One leaders Cove Rangers.
With Paul Hartley's side held to a draw, Airdrie closed the gap at the top to five points and stretched their lead over third-placed Montrose to four points.
Calum Gallagher's first-half double was halved by a Graham Webster penalty, but though the visitors started the second period as the better side, Airdrie soaked up the pressure and struck decisive blows via sub Craig Watson and Adam Frizzell.
The Diamonds took a 2-1 lead into the interval and Calum Gallagher was on target with both for his eighth and ninth goals of the season.
He struck in 34 minutes, when the striker simply picked up possession outside the box and curled a delightful shot into the top right corner.
Two minutes later, a sweeping move down the left led to Gallagher back-heel flicking the ball in off the underside of the crossbar.
But Montrose were handed a lifeline when Blair Lyons was tripped by Adam Frizzell to earn a penalty, which Graham Webster buried.
Montrose stepped it up in the second half and went close through Lyons and Webster, but Airdrie extended their lead, somewhat against the run of play, in 64 minutes when Watson sent a shot high into the net.
But Frizzell struck and then headed in the rebound to put Airdrie 4-1 up in 70 minutes after Montrose keeper Allan Fleming had superbly saved his initial effort.
Airdrie boss Ian Murray made one changes to the side that drew 1-1 at Cove Rangers last weekend, with Calum Gallagher coming in for Jordan Allan up front.
New signings Justin Devenny, on loan from Kilmarnock, and Jon Afolabi, on a similar deal from Celtic, had to settle for places on the bench.
Montrose gaffer Stewart Petrie made two changes to his side that also drew 1-1 with Dumbarton. Matty Allan and Lewis Milne came in for Aidan Quinn and Michael Gardyne.
The last time these sides faced off at this venue, Montrose ran out comfortable 3-0 winners. Stewart Petrie's side also won 2-1 at home back in December.
Ahead of the game, second-placed Airdrie and their visitors were separated by a single point, so there was a lot riding on this.
The first effort of note came in 10 minutes through Montrose's Blair Lyons, whose low shot was deflected past the right post.
AIrdrie's first real effort on goal came two minutes later but Rhys McCabe's hot flew harmlessly wide of the left post.
The hosts should have taken the lead in 16 minutes when Brody Paterson got the break of the ball from a Matty Allan challenge and raced down the left, but his cutback was inches too far ahead of Callum Smith, who was stretching to meet it in the middle.
But Airdrie took the lead when Gallagher picked up possession about 22 yards out and curled a delightful shot into the top right corner.
Two minutes later a sweeping Airdrie move sent Dylan Easton down the left and his cross was back-heel flicked in via the underside of the crossbar.
But Montrose were thrown a lifeline on the stroke of half-time when they were handed a penalty.
Blair Lyons darted into the box and looked to go over Adam Frizzell's challenge, with referee Lorraine Watson immediately pointing to the spot.
Graham Webster stepped up and slotted the spot-kick into the bottom left corner, but was then booked for following the ball into the net and remonstrating with goalkeeper Max Currie.
Montrose should have levelled in 47 minutes when Webster's cross from the right was met by Lyons at the left post, but Currie made a great block to deny him.
A minute later, Gallagher threaded the ball through to Smith in the box, but a superb saving tackle denied him.
Webster had a go from distance in 58 minutes but saw his rising shot punched away by Currie.
But Airdrie extended their lead in 64 minutes when Paterson tore down the left and crossed for sub Watson to meet it with a crisp shot and send it beyond Allan Fleming.
Smith turned provider six minutes later when his cross picked out Frizzell and his shot was well saved by Fleming, but the former Killie star followed up to head into the net.
AIRDRIE: Currie, MacDonald (Watson, 46), Kerr, Fordyce, Paterson, Agnew, McCabe, Easton (S. McGill, 85), Frizzell (Devenny, 89), Gallagher (Afolabi, 76), Smith (Allan, 89).
Subs (not used): Cantley (GK), Ritchie, Walker, G. McGill.
Booked:
MONTROSE: Fleming. C. Ballantyne, Allan, Dillon, Steeves, Milne (Whatley, 74), Masson (Simpson, 70), C. F. Ballantyne (Baxter, 81), Webster (Campbell, 81), Johnston (Brown, 74), Lyons.
Subs (not used): Lennox (GK), Belford, Houghton, Giacomini.
Booked: Dillon (29), Webster (45), Milne (74), C. Ballantyne (90)
Referee: Lorraine Watson.
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