Match ends, Airdrieonians 0, Dundee United 1.
Blair Spittal curled in a wonderful free-kick as Dundee United broke down Airdrieonians' stubborn resistance to reach the last 16 in the Scottish Cup.
The League One hosts started brightly but the Premiership's bottom side took control after the interval.
Paul Dixon hit the crossbar in the first half, with Billy McKay and Scott Fraser also going close.
And Spittal struck on 79 minutes to end a sequence of nine games without a win for Mixu Paatelainen's men.
A small band of visiting supporters spilled on to the artificial surface at the Excelsior Stadium to join the celebrations, having had little to cheer this season.
With United 11 points adrift in the top flight, Airdrie perhaps sensed an early vulnerability.
The Premiership side found it difficult to cope with the long throw-ins from Jamie Bain and Eiji Kawashima made a point-blank save from Marc Fitzpatrick before tipping a Bryan Prunty header over the bar.
Prunty then sent a back-post header into the side-netting before United began to dominate possession.
The 2010 Scottish Cup winners winners hit the woodwork when Dixon cut in from the left flank to flight a shot towards the far corner. The rebound fell to Spittal but the midfielder's low strike was well saved by Rohan Ferguson.
The teenage keeper, standing in for suspended Neil Parry, would be much busier in the second half as the Diamonds were put under increasing pressure.
Dixon, always prominent, flashed a great delivery across goal, with McKay shooting into the side-netting soon after.
Another good Dixon cross was met by Fraser on the volley but the former Airdrie loanee's effort thumped into the astroturf and spun over the crossbar.
Ferguson then touched away Fraser's low drive and, from the corner, the hosts survived an almighty scramble.
United were rewarded for their dominance when Spittal sent his free-kick into the top corner, with Ferguson barely moving as he watched the ball ripple the net.
The visitors continued to hog the ball and the only chance to come the way of Airdrie in the closing minutes saw Liam Watt shoot tamely at Kawashima.
- 7CoxBooked at 80minsSubstituted forMorganat 83'minutes
- 9ListerSubstituted forMackinat 59'minutes
- 10PruntySubstituted forBrownat 83'minutes
- 28DonaldsonSubstituted forPatonat 87'minutes
- 11ErskineSubstituted forRiskiat 67'minutes
- Greg Aitken
- Shots on Target
Second Half ends, Airdrieonians 0, Dundee United 1.
Substitution, Dundee United. Paul Paton replaces Coll Donaldson because of an injury.
Corner, Dundee United. Conceded by Marc Fitzpatrick.
Coll Donaldson (Dundee United) wins a free kick in the attacking half.
Foul by Dylan Mackin (Airdrieonians).
Attempt saved. Liam Watt (Airdrieonians) right footed shot from the centre of the box is saved in the top left corner.
Substitution, Airdrieonians. Adam Brown replaces Bryan Prunty.
Substitution, Airdrieonians. Taylor Morgan replaces David Cox.
Foul by Guy Demel (Dundee United).
Liam Watt (Airdrieonians) wins a free kick in the attacking half.
David Cox (Airdrieonians) is shown the yellow card for a bad foul.
Mark Durnan (Dundee United) wins a free kick on the right wing.
Foul by David Cox (Airdrieonians).
Goal! Airdrieonians 0, Dundee United 1. Blair Spittal (Dundee United) from a free kick with a right footed shot to the top left corner.
Scott Fraser (Dundee United) wins a free kick in the defensive half.
Foul by Liam Watt (Airdrieonians).
Hand ball by Dylan Mackin (Airdrieonians).
Coll Donaldson (Dundee United) wins a free kick on the left wing.
Foul by Bryan Prunty (Airdrieonians).