The home side managed to draw first blood when fly-half Andy Dunne burst through to send England centre Will Greenwood over a try in the fifth minute.
But from then on in, it was pretty much one-way traffic – with the Saints' back row threesome of skipper Corné Krige, Andrew Blowers and Grant Seely proving to hot to handle.
It was the No.8 Seely who got the rout underway by showing the footwork of a half-back to exploit some shoddy defending and touch down between the posts.
Next up, Greenwood and Dunne were left standing as new Saints centre Marc Stcherbina steamed through before off-loading to Blowers, who sent Johnny Howard over for the try.
Then Howard returned the favour by delivering a superb reverse pass to Blowers, who dispatched England wing Ben Cohen on a straight run-in under the posts.
Former England fly-half Paul Grayson and former All Black fullback Bruce Reihana then combined to send wing John Rudd over into the right corner on the stroke of half-time .
Northampton increased their lead to 34-8 after the break when centre Mark Tucker made the most of a three-man overlap to touch down.
Mass substitutions by both sides interrupted the flow of the game but Northampton picked up the pace again with their replacements getting in on the act.
Shane Drahm, on for Grayson, kicked two penalties and Darren Fox, who took over from Blowers at half-time, forced his way over for a 73rd-minute try.
Rudd was then shown a yellow card for a high tackle on winger Ugo Monye, who promptly took his revenge with a try at the death – but that was of scant consolation to the home fans.
For NEC Harlequins:Tries: Greenwood, MonyePen: Dunne
For Northampton Saints:Tries: Seely, Thompson, Cohen, Rudd, Tucker, Fox Cons: Grayson 3Pens: Grayson, Drahm 2