Fleetwood’s standing as the best away side in league two was dismantled at Sixfields as the Cobblers recorded a sixth win their past seven home league games.
Chris Hackett supplied crosses for two goals, scored by Jake Robinson and Clive Platt, and Alex Marrow put through his own net in a comprehensive 3-1 victory.
Jamie Allen scored an injury-time consolation for the visitors, who came into the game having only lost twice away from home this season.
The win lifts Town to ninth in the npower League Two standings, just a point outside the play-off places and four behind third-placed Rotherham United.
To record such a comfortable victory against a team who have been in the top seven all season also represents a big statement of intent from Aidy Boothroyd’s men, who have not lost in the league since December 8.
Less than eight minutes had been played when the home side made their mark, Ben Tozer winning a header powerfully at right-back and Platt doing likewise in the centre circle only to find the ball returned to him, from where he sought out Chris Hackett with an excellent volleyed pass.
Hackett’s looped cross from the right was beyond Akinfenwa but not Robinson, who planted a copybook standing header across Scott Davies and into the far corner of the net.
Robinson almost had an instant second when his left-footed shot was blocked by his marker after more good work down the right by Hackett.
The right-winger then almost break in behind but Fleetwood’s talented full-back Dean Howell matched him stride for stride down the inside-right channel and did enough to prevent any kind of attempt at goal.
Robinson will claim the second goal too, but his shot from the edge of the box took two deflections - the second off central midfielder Alex Marrow before rolling across the line.
Town almost had a third in first-half stoppage time when Luke Guttridge attempted a lob from the edge of the box after a goalmouth scramble only to see his attempt bounce on top of the bar.
The visitors started the second half brightly with Lee Nicholls making his first save of the game but soon found the ball swiftly deposited in their net for a third time.
Again Hackett was involving, providing another superb cross for Adebayo Akinfenwa to head down, Davies palmed it away but Platt reacted quickest to get to the ball before the covering defender and crash a shot into the roof of the net.
Akinfenwa himself then almost made it four with a more traditional Northampton attack, heading narrowly over directly from Tozer’s long throw.
Rather than seek enhanced goal difference during the game’s final third the Cobblers were content to play at half-pace and let their opponents have the ball for long spells.
The match was deprived of a testimonial atmosphere, though, by the antics of visiting midfielder Marrow, who played pantomime villain for the west stand with a serious of spiky challenges.
Louis Moult found himself in a good position to shoot with five minutes to go but got caught in two minds and ended up floating a pass harmless out of play and Hackett sidefooted one that Davies held well in the Fleetwood goal.
In injury time Jamie Allen gave the result a degree of respectability with an acrobatic volley after Carlisle had failed to clear with a header.
But to have won by more might have been greedy anyway. This was enough of a statement to the rest of league two without the added emphasis of an embarrassing scoreline.
Cobblers: Nicholls, Tozer, Langmead, Carlisle, Widdowson, Hackett, Guttridge, Harding, Robinson, Akinfenwa, Platt
Subs: Hornby (for Guttridge 74), Moult (for Platt 78), Demontagnac (for Robinson 83)
Not used: Charles, Snedker, Wilson, Turnbull
Fleetwood: Davies, McLaughlin, Atkinson, Goodall, Howell, Johnson, McGuire, Marrow, Brown, Ball, Titchiner
Subs: Barry (for McGuire 46), Evans (for Johnson 46), Allen (for Ball 77)
Not used: McNulty, Milligan, Maxwell, Gillespie
Away fans: 118
Referee: Rob Lewis