The hosts had to come from behind to finally banish the barren run, which has lasted since the opening day of last season.
David Sinclair fired Airdrie ahead, but the visitors turned the match on its head through Chris Aitken’s penalty and Martin Grehan’s header.
Airdrie weren’t to be denied, though, with Lewis Coult equalised before Buchanan’s winner. Manager Jimmy Boyle said: “You have to praise the players for the character they showed to get back into the game and then keep on going until we got the winner.”
Stranraer manager Stephen Aitken said: “We deserved at least a draw.”
Dunfermline fell five points behind leaders Rangers after Brechin hit back to grab a 1-1 draw at Glebe Park. The Pars had led through Robert Thomson, but Andy Jackson equalised in the second half.
Stenhousemuir remain third on the same ten-point mark as Dunfermline after drawing 1-1 with Ayr United, whose player-manager Mark Roberts curled home from 18 yards, only for the Warriors to hit back through Darren Smith.
Forfar notched their first league win as they triumphed 3-1 at East Fife. James Dale gave the Loons the lead, but Scott Durie equalised. Dale Hilson and Gavin Swankie sealed the points for the visitors.