Ishmel Demontagnac became the fourth Cobblers player sent off in as many away matches as Town exited the Johnstone’s Paint Trophy at the hands of Milton Keynes Dons.
Demontagnac saw red for a bad challenge on Dele Alli in the closing stages of the first half and, in the second, the home side capitalised on the man advantage to score twice.
Alli himself was joined on the scoresheet by Patrick Bamford as the Dons ran out 2-0 winners and secured a fifth loss of the season for Northampton, in six games.
Milton Keynes almost took the lead in fortunate circumstances after 24 minutes when Jason Banton evaded Ben Tozer down the left wing and sent in a cross that was deflected and spun away from Matt Duke and onto his post.
Bamford looked to follow up the rebound but Duke did well to recover and smother it away to safety with Lee Collins completing the clearance.
The game’s flashpoint came on 34 minutes, when Tozer played a superb crossfield pass to Demontagnac on the left side that the winger made a mess of controlling, spilling the ball to Alli, who broke away with it.
As has been the case on a number of occasions, the red mist descended on Demontagnac and he produced what was nothing more than a blatant kick on the calf of the teenager, an indiscretion for which he was rightly – and swiftly – shown the red card.
The setback seemed to help the Cobblers, who made a bright start to the second half and forced a good save out of Ian McLoughlin from a good run and left-footed shot by Jacob Blyth.
But moments later the home side had found a breakthrough. A cross from the left was deflected and squirmed past Duke at the front-post area for Bamford to tap in unmarked in the six-yard box.
The lead was doubled seven minutes later when a rash tackle in midfield saw the ball worked to Jason Banton down the right, from where he had plenty of time to pick a pass for Dele Alli to drive into the roof of the net with a first-time shot from 16 yards.
The Cobblers had plenty of the ball after the goal, although with the game won and Milton Keynes happy to stand off their opponents, this was almost a given.
Such a policy cost the Dons a goal through Roy O’Donovan at Sixfields and it nearly led to one for Blyth in this game.
The Leicester loanee skipped through the defence until he was one-on-one with McLoughlin and then sidefooted wide of the post when it looked as though the goalkeeper was resigned to the goal.
A failure to capitalise on the slim chances that came the Cobblers’ way, however, was not the primary reason for the defeat. Again, it was discipline that was the difference.
Milton Keynes Dons: McLoughlin; Otsemobor, Williams, Kay, Lewington; Green, Reeves, Smith, Banton; Alli; Bamford
Subs: Chadwick (for Alli 71), Baldock (for Green 78), Galloway (for Williams 83)
Not used: Rasulo, Carruthers
Cobblers: Duke; Tozer, Collins, Heath, Amankwaah; Hackett, Deegan, Carter, Harriott, Demontagnac; Blyth
Subs: Emerton (for Hackett 64), Toney (for Deegan 85), Hooper (for Harriott 89)
Not used: Snedker, Platt
Cobblers fans: 861
Referee: Graham Horwood