The impressive Davis Keillor-Dunn scored two excellent goals to ease Barnsley into a 2-0 lead on the hour, and it looked as though they would coast to victory.
But the Cobblers hit back with a Sam Hoskins strike on 78 minutes, and although they then pressed for an equaliser, they couldn’t square things up.
The defeat leaves Town in 17th in the league one table, four points above the relegation zone.
Here are Jeremy Casey’s player ratings.
1. Nik Tzanev
Beaten by two excellent strikes from Keillor-Dunn that gave him little chance, Tzanev did also produce a couple of key stops... 6 Photo: Pete Norton
2. Sam Hoskins
As always, Hoskins' heart and commitment can never be questioned. Another lung-busting evening covering so much ground, and another goal too, producing a thumping close-range finish.. 7 Photo: Pete Norton
3. Jordan Willis
Was part of a back three that on two occasions afforded the dangerous Keillor-Dunn too much space for his goals... has been struggling with injury and looked a little sluggish.. 6 Photo: Pete Norton
4. Akin Odimayo
Odimayo had his evening ended early by injury which is hopefully nothing too serious. The combative defender had turned in a decent performance prior to that... 6.5 Photo: Pete Norton