Both goals came in a first half that Quakers barely contested although after the break Steve Staunton's side showed some determination to pull a goal back.
Despite going close several times the bottom-of-the-table side could not mount a comeback and so sank to their 14th away defeat.
Coupled with Cheltenham Town's remarkable 6-5 win at Burton Albion, Quakers are now 18 points from safety with 13 games to play so it is surely only a matter of time before they are officially relegated.
Hopes of mounting a great escape have not been high for sometime, though back in January they took the lead against Northampton when there was still a slim chance of avoiding the drop.
Northampton went on to beat Quakers 2-1 that night at the Arena with Billy McKay scoring one of the goals and today's first chance fell to the striker.
A Northampton corner looped into Quakers' penalty area and found the unmarked McKay at the near post but his volley was well held by keeper Shane Redmond.
Darlington were again using the 4-3-3 formation that worked so well in Tuesday's 1-1 draw at Bury, but in the early stages at Sixfields Staunton's side were finding it tough to mount attacks.
Little supply was reaching the front three of Mor Diop, Tadhg Purcell and Curtis Main and that meant Darlington's defence were under constant pressure.
On 20 minutes the defence cracked with right-back John Johnson scoring. He reacted quickest to poke home the loose ball after Adebayo Akinfenwa's shot had rebounded off the crossbar.
Johnson, on loan from Middlesbrough, started the move by playing in Akinfenwa who had evaded Darlington's Alan White but the striker's shot hit the woodwork before his team-mate tapped in to make it 1-0.
The strike was the youngster's fourth in Northampton colours during his season-long loan from Teesside, but his Boro team-mate Jason Steele had little to occupy him in goal.
The keeper saw little of the ball during the first half though he should have been given a shot to save on the half hour mark.
Simon Madden's cross from the right was met by Gareth Waite but from a tight angle the former Spennymoor midfielder headed wide.
Six minutes before the break it became 2-0 with Abdul Osman scoring following a corner.
Liam Davis' flag kick was met by Akinfenwa whose header was partially punched clear by Redmond and the ball fell to Johnson who played in Osman to slot home from 12 yards.
It was little more than the hosts deserved at the end of a half in which they were rarely troubled and before the break they almost had another goal.
Davis is Cobblers' dead-ball specialist and a minute before the break he was inches away from making it 3-0 with a free-kick.
From 25 yards he curled an effort narrowly wide of Redmond's left-hand post and within ten minutes of the restart the midfielder tried again from similar distance.
This time his effort rolled wide of goal. He might have missed but at least he was attempting to score whereas Steele remained underemployed in the Northampton goal.
On 55 minutes he was called on to catch an optimistic Purcell volley from long-range but that effort heralded the beginning of something of a Darlington fightback.
At the break Staunton had switched to 4-4-2, sending on wingers Josh Gray and Chris Moore. Soon Gray beat Johnson on the left before delivering a cross that was intercepted.
Then Moore, the 51st different player used by Darlington this season, ran down the right but his ball into middle was cut out by Craig Hinton before pressure from Diop almost saw Steele lose possession.
The keeper then escaped for a second time. He spilled Andrew Milne's 20-yard drive but gathered the ball just as Gray was about to pounce.
Quakers showed much more fight in the second half with their new formation causing the Cobblers problems with Gray swinging in another cross but Purcell could only head wide.
With 20 minutes to play two substitutions were made with Patrick Deane sent on for Diop while referee Andy Penn had to leave the field with an injury and he was replaced in the middle by a linesman.
Darlington kept pushing and on 79 minutes Waite dispossessed Alex Dyer on the edge of Northampton's penalty area but saw a powerful strike sail wide of the far post With five minutes to go Quakers hit the woodwork from a corner. Gary Smith swung the ball over to the far post where Purcell's downwards header bounced away off the upright.
Gray intercepted ball and dribbled into Northampton's penalty area before seeing a powerful shot parried by Steele and Johnson was first to the loose ball ahead of Deane.
In injury time Darlington continued to go for goal but the closest they came was a Purcell header, from a Moore cross, directed too close to Steele.
Darlington do not have a midweek match so their attentions turn to next Saturday's home game with Barnet.
Goals: Johnson (20, 1-0), Osman (39, 2-0)
Bookings: None
Referee: Andy Penn (West Midlands)
Attendance: 4,755
Northampton Town (4-4-2): Steele; Johnson, Hinton, Beckwith, Gilbert; Rodgers, Osman, Dyer, Davis (Guttridge 80); McKay, Akinfenwa. Subs (not used): Walker (gk), Mulligan, Jacobs, Herbert, Harris, O'Flynn
Darlington (4-3-3): Redmond; Madden, White, Miller, Milne; G Smith, Waite; Dempsey (Gray 45); Purcell, Diop (Deane 71), Main (Moore 45). Subs (not used): Liversedge (gk), Burn, Mulligan, Chisholm
Source: Northern Echo
>> Terms & Conditions