Despite the scoreline, Gretna were made to work hard for their Challenge Cup victory at New Broomfield.
The visitors opened the scoring after 12 minutes when Allan Jenkins' throughball was misjudged by Marc Smythe and Kenny Deuchar volleyed in.
Airdrie's Bryan Prunty saw a header cleared off the line just a minute after the restart.
But Gavin Skelton crossed for Paul Tosh to fire home on 71 minutes and Deuchar struck soon after with a low shot.
Airdrie Utd: Hollis, McKenna, McGowan, Smyth, Christie (Tierney 55), Holmes, McDougall, McKeown, McPhee (Watson 78), Twigg (Prunty 46), McLaren. Subs Not Used: Stokes, Robertson.
Gretna: Mathieson, Birch, Nicholls (McGuffie 59), Skelton, Townsley, Canning, McGill, Jenkins (Tosh 59), Deuchar, McMenamin (Graham 78), Granger. Subs Not Used: Berkeley, Fleming.
Booked: Granger. Goals: Deuchar 12, Tosh 71, Deuchar 76.
Ref: K Clark