Airdrie left it late to complete a dramatic comeback and claim all three points by beating 10-man Forfar.
Christopher Templeman broke the deadlock for the hosts after 15 minutes, weaving his way into the area to tap home from six yards.
The Loons doubled their advantage three minutes later as Kevin Motion seized on Graham Gibson's crossfield ball to volley beyond Paul McKane from the edge of the area.
But Sean Lynch reduced the deficit shortly before the break as he collected William McLaren's pass to coolly beat Jamie Langfield.
And McLaren had the Diamonds level on the stroke of half-time, finishing Jamie Stevenson's looping cross at the near post.
Christopher Hegarty was then dismissed for a professional foul on Lynch in the 64th minute, but Stevenson was unable to make the resulting free-kick count, with Langfield making the save.
And the visitors' numerical advantage ultimately paid dividends three minutes into added time when substitute Scott Morton clipped home with his left foot to seal a last-gasp victory.
Forfar: Langfield, McCulloch, Shaughnessy, Bolocheweckyj (Mowat 46), Iain Campbell, Hegarty, Ross, Byers (Ross Campbell 46), Motion, Gibson (Low 70), Templeman. Subs Not Used: Paterson, Tulloch.
Sent off: Hegarty (64).
Booked: Bolocheweckyj, Shaughnessy.
Goals: Templeman 15, Motion 18.
Airdrie Utd: McKane, Green, Stallard, Lilley, Goodall, Lynch, Bain, Blockley, McLaren, Stevenson, Donnelly (Morton 87). Subs Not Used: Fairley,Boyle,Owens,Keast.
Goals: Lynch 42, McLaren 45, Morton 90.
Referee: Kevin Clancy