Darren Carter scored a second-half penalty to secure a draw for the Cobblers against a Mansfield side that played for half an hour with 10 men.
Town did not take advantage of the extra man and settled for a 1-1 stalemate that extends their unbeaten run to six games.
It will, however, go down as an opportunity missed, even if fellow strugglers Accrington, Wycombe, Portsmouth and Bristol Rovers were all beaten.
Exeter City, to whom the gap is now two points, play Newport County on Sunday.
Town were in behind Mansfield’s defence within two minutes of the game starting, Alan Connell spraying a pass for Brennan Dickenson to race onto and fire a left-footed effort straight at the advancing Alan Marriott.
The rebound fell straight to the winger but on his weaker right foot his effort was blocked by the covering defender with some ease.
Mansfield, though, had their chances - Chris Hackett had to be in the right place to head an effort from close to the goal line and Lee Stevenson should have done better with a blocked shot after finding space in the box.
And they took the lead on 32 minutes, Matt Rhead playing strike partner Oliver Palmer in behind the home defence.
Matt Duke stayed on his line, Mathias Doumbe hesitated and Palmer sidefooted the ball under the goalkeeper to put the Stags in front.
Town’s response was a muted one but they almost gained an advantage in the game when Martin Riley fouled Dickenson on the edge of the box at the end of a counter-attack.
The home crowd, predictably, wanted a red card for Riley but there was a covering player and the defender was booked, with Darren Carter hitting the free-kick into the defensive wall and Ricky Ravenhill thrashing the rebound over the bar.
Hackett saw an effort deflected wide after Carter had expertly threaded in Dickenson down the left and Emile Sinclair had held up play in the box.
Ian Morris was a lively introduction minutes after the interval and drew a good save from Marriott with a right-footed shot on the edge of the area.
Then came the controversy. A Hackett cross into the box was met at the back post by Connell but he was denied clean contact on the ball by Westlake, who punched the ball away.
Referee Andy Haines spotted it and awarded a penalty, sending right wing-back Westlake off in the process.
Although Marriott went the right way, Carter’s spot-kick had enough power on it to beat the goalkeeper and draw Northampton level.
Town’s best chance to win it came at the end of a Morris-led counter-attack, when Connell flighted a cross for Hackett to volley over at the back post.
But they did not have a long period of pressure at any point and did not create any other good chances.
Cobblers: Duke, McSweeney, Doumbe, Diamond, Robertson, Hackett, Ravenhill, Carter, Dickenson, Connell, Sinclair
Subs: Morris (for Dickenson 50), Lopez (for Hackett 88)
Not used: Snedker, Deegan, Tozer, Toney, Moyo
Mansfield: Marriott, Riley, Dempster, Tafazolli, Westlake, Howell, Murray, Stevenson, Jennings, Rhead, Palmer
Subs: Daniel (for Palmer 68), Meikle (for Stevenson 68), Dyer (for Rhead 85)
Not used: Briscoe, Beevers, McGuire, Cain
Away fans: 744