Simon Ainge's 11th minute effort nestled into the net via a combination of post and Jackson as United suffered a third away defeat of the campaign.
Ben Middleton received his marching order eight minutes later while keeper George Willis was red-carded with five minutes to play as United's afternoon ended disappointingly.
There had been little sign of the drama to follow during a quiet opening at Blackwell Meadows.
The match finally ignited when the dangerous Harvey Saunders burst down the left to whip over a cross which Ainge rattled against the post and the ball nestled into the net off the unlucky JACKSON.
United’s afternoon took a further downturn when Middleton flew into a challenge on Jordan Nicholson in the centre circle and duly received his marching orders.
The Pilgrims kept Darlo at arm’s length for the remainder of the half and carved out a trio of chances in the closing stages.
Josh Hine was unable to get enough purchase on a Ben Davies cross to the near post while Jonny Maddison got behind a Gavin Allott drive before tipping Davies’ arrowing free-kick behind for a corner.
United should have levelled four minutes after the break when Allott met Davies’ free-kick but his header dropped agonisingly wide.
Willis saved well to deny Saunders before dashing from his area to upend the same player in the 85th minute and receive United’s second red card of the game.
Sebastian Malkowski emerged from the bench to make his United debut and subsequently made an excellent save to keep out Stephen Thompson’s long-range stinger.
Darlington (3-5-2): Jonny Maddison; Luke Trotman, Liam Hughes, Terry Galbraith; Stephen Thompson (Cialan Banks 90), Tom Elliott, Jordan Nicholson, Joe Wheatley, Alex Henshall (Jonny Burn 54); Simon Ainge, Harvey Saunders (David Syers 90). Subs (not used): Mitchell Glover, Aaron Burn (gk).
Boston (4-4-2): George Willis; Ben Davies, Ryan Qualter, Ben Middleton, Ashley Jackson; Josh Hine (Max Wright 84), Brad Abbott, Andi Thanoj, Nicky Walker; Gregg Smith (Andre Johnson 63, Sebastian Malkowski 87), Gavin Allott. Subs (not used): David Norris, Jordan Slew.
Referee: Paul Brown.
Attendance: 1,345.