They made the best possible start by going ahead after only two minutes when Mark Baxter's free-kick was knocked down by Ryan McCallum for Buchanan to head home bravely from close range.
Jackson's header then clipped the top of the Arbroath crossbar and when the visitors were reduced to ten men after Paul Watson picked up his second yellow card barely five minutes after the first, Cowdenbeath looked in complete control.
But Arbroath grabbed a bizarre equaliser as a corner kick bounced off the head of Pat Clarke and trickled over the line as the home defence stood and watched.
Keeper David Hay made an excellent save from Jay Stein's sweetly struck free-kick shortly before half-time and Steven Cook then fired Arbroath into a shock lead after 61 minutes, following a bad mistake by defender John Ward.
Cowdenbeath were suddenly facing a humiliating and expensive defeat, but Buchanan had other ideas and quickly made it 2-2 with an angled half volley from just inside the penalty area.
Two minutes later Jackson shot first time through a forest of legs to give the home side the result that they wanted.