Arbroath are now seven points behind Scottish Second Division leaders Cowdenbeath after late goals from Paul Lovering and William McLaren condemned the title-chasers to a defeat at Airdrie.
The Red Lichties had gone 12 games without defeat and almost went behind after 10 minutes, Jamie Bain forcing Darren Hill into a good save with a curling shot from the edge of the area before John Boyle's volley drew another great save from Hill six minutes later.
Arbroath's best chance fell to substitute Craig Wedderburn, who headed over from close range nine minutes into the second half before Paul Sheerin's men went behind, Lovering heading McLaren's corner past Hill after 73 minutes.
McLaren secured the Diamonds' victory in the 94th minute with a thumping volley from the edge of the area.
Airdrie Utd: Adam, McNeil, Lilley (Lamie 90), Stallard, Lovering, Bain, Lynch, MacDonald, Donnelly (Keast 87), McLaren, Boyle (Holmes 66).Subs Not Used: Duncan, Watt.
Booked: Lynch, Lovering.
Goals: Lovering 73, McLaren 90.
Arbroath: Hill, Baxter (Sibanda 46), Malcolm, Innes, McAnespie (Wedderburn 26), Falkingham, Kerr, Caddis, Sheerin, Doris, Mair (Samuel 67).Subs Not Used: White, Gibson.
Ref: Gary Hilland