Goals from former Bees forwards Sam Hoskins and Ricky Holmes helped to sink Barnet, as they succumbed to a 3-0 defeat at Sixfields.
The Cobblers took an early lead through Hoskins, before Holmes burst through to fire home a second in the 52nd minute.
High-flying Northampton made sure of the win when top scorer Marc Richards struck a well-placed effort mid-way through the second half.
It was always going to be tough for the Bees, when they found themselves a goal down with just four minutes on the clock.
Barnet’s defence failed to clear a cross from the left, and Hoskins slotted the ball past Ian Lawlor and into the bottom right corner of the net.
The on-loan keeper made a spectacular double save five minutes later – stopping Holmes and Richards’ goal bound efforts in quick succession.
John Akinde had Barnet’s first chance of the match when he headed a cross straight at Adam Smith after ten minutes.
After a frenetic opening period the remainder of the first half was short of clear-cut chances.
Northampton thought they had a penalty just before the break, but referee Ross Joyce waved away Brendan Moloney’s claims after he went down in the box.
However the Cobblers doubled their lead within seven minutes of the restart – Holmes was played through and fired a powerful shot past Lawlor and into the net.
Richards’ added a third with 59 minutes on the clock when he finished neatly into the bottom left corner.
Akinde cut the ball back to Curtis Weston two minutes later, but his shot flew high over the bar and out for a goal kick.
Northampton began playing with the confidence that goes alongside a three goal lead, and had a handful of chances to add to their advantage.
Lawlor got down to his right to stop Lawson D’Ath’s drive in the 62nd minute, before tipping Holmes’ 67th minute shot around the post.
The latter stages at the match saw the Bees try to get back into the game, but they struggled to break down a resilient Northampton rear-guard.
Martin Allen’s side now return to The Hive for back-to-back home matches – they face Bristol Rovers and Carlisle United in the next fortnight.
BARNET: Lawlor, Johnson, N’Gala, Dembele, Yiadom ©, Togwell, Weston (Odoffin 71’), Champion (Hoyte 57’), Gambin, McLean (Batt 57’), Akinde.
Unused Subs: McKenzie-Lyle, Gash, Lisbie, Muggleton.