Andy Robinson scored for the third game running as Swansea City took another step closer to the League One play-offs.
Despite falling behind early to a sixth-minute Brad Johnson strike, Dennis Lawrence fired home the equaliser on the stroke of half-time to lift Swansea for the second-half.
Robinson struck the winner just 25 seconds in to fire Swansea up a place to seventh and stretch Roberto Martinez's unbeaten start in the managerial hot-seat to five games.
Swansea City: Gueret, Amankwaah, Painter, Iriekpen, Lawrence, Britton, Tate (c), Craney, Robinson, Abbott, Butler. Subs: Oakes, Jones, Williams, O'Leary, D Duffy.
Northampton Town: Bunn, Crowe, Holt, Hughes, Doig (c), Deuchar, Hunt, Johnson, Pearce, Robertson, Gilligan. Subs: Dunn, Taylor, Kirk, Aiston, Cox.
Ref: K P Stroud
Asst-refs: A S Watts, A J Horton
4th official: R Smith
Att: 11,071
FirstPlus Man of the Match: Tom Butler
Swans boss Roberto Martinez named an unchanged side from the one that beat Leyton Orient 2-0 last Friday at the Liberty Stadium.
It meant new loan signing Darryl Duffy from Hull started on the subs bench along with midfielder Kristian O'Leary who had recovered from an ankle injury.
Pawel Abbott remained as the lone striker up front, with Andy Robinson, Leon Britton and Tom Butler offering plenty of attacking options just behind.
Lee Trundle sat out his last game through suspension, while Richard Duffy was away on Wales duty.
Swansea, going into the game in eighth place and just one point off the play-offs, faced a Northampton side in 15th place.
Although Swansea made a bright opening, they couldn't have wished for a worst start as they fell behind to a stunner after just six minutes.
Ian Craney conceded a foul just over 30 yards out and Brad Johnson unleashed a fierce free-kick which flew like an arrow into the roof of Willy Gueret's net with the Swansea 'keeper motionless.
Swansea tried to get themselves back into the game, but despite enjoying plenty of possession, they came up against a Cobblers side who were putting plenty of players behind the ball.
Abbott nearly played Britton in with 20 minutes gone as Swansea were encamped in the visitors' half, but again there was a claret shirt to block the pass on the edge of the area.
Butler did force Mark Bunn into his first save a minute later as he pushed his shot around the post from 20 yards, but Craney wasted the corner.
Swansea came back again and had n appeal for a penalty turned down when Abbott was bundled over by Alex Pearce as he tried to connect with a Butler cross.
But just when Swansea looked to be heading in at the break a goal down, big Dennis Lawrence gave them a lifeline three minutes into injury time.
Alan Tate saw his 25 yard shot blocked on the edge of the area, but as the ball dropped Lawrence fired a right foot shot into the far corner.
Half-time: Swans 1 Cobblers 1
Lawrence's equaliser had the desired effect as Swansea were ahead for the first time within 25 seconds of the second half.
Abbott's neat flick sent Butler racing down the right wing to the edge of the area. His low cross eluded the oncoming Britton, but not the supporting Andy Robinson who fired into the roof of the net from eight yards.
The Swans were given a timely warning two minutes later, however, that the game still had to be won as Johnson struck the Swansea bar with a fierce shot from the edge of the area.
Good skill from Craney eventually saw Butler make another positive attack down the right. The Republic of Ireland international cut inside and unleashed a fierce shot which just flew over Bunn's bar.
Swansea nearly threw their lead away in the 61st minute though when Gueret came and missed a punch on the edge of the six-yard area.
As the ball dropped, the unmarked Kenny Deuchar looked odds on to score, but somehow Izzy Iriekpen managed to get a foot to his goal-bound shot to save the day.
Midfielder Kristian O'Leary came off the substitutes bench three minutes to replace the injured Kevin Amankwaah as Swansea were forced to reshuffle with Alan Tate moving to right back.
Butler was having a great game on the right as he drilled in another dangerous cross to the far post where Robinson was waiting. The midfielder drove his cross across the face of goal, but it just eluded Britton.
It was the last part Robinson was to play as he was replaced in the 67th minute by new loan signing Darryl Duffy - the HullCity striker making his Swans debut.
Butler was also replaced in the 77th minute by Tom Williams as the Swansea manager looked for fresh legs as Northampton started to commit more men forward.
As the game opened right up, Britton raced clear down the right. His pass found Craney inside and the midfielder unleashed a fierce shot from 25 yards which Bunn did well to beat out.
Iriekpen thought he had scored for the second game running with five minutes remaining as he moved forward for a corner, but his shot was blocked on the line by Mark Hughes. Swansea claimed a handball, but the referee waved play on.
Not that it mattered as Swansea stretched their unbeaten run under new manager Roberto Martinez to five games - four of which ended in victory.
