Ashton is making a big impact after his switch from rugby league
Northampton winger Chris Ashton enhanced his growing reputation with a hat-trick of tries as Saints secured a fourth straight win.
The former Wigan rugby league back crossed once before the break after fine work by Shane Geraghty and touched down twice more in the second half.
Geraghty, back from England duty, was on fine form and added three penalties and two conversions for the visitors.
Tom Biggs grabbed the only try for the hosts on a bitterly cold night.
Newcastle had been caught napping when Northampton took a quick tap in front of the sticks early on.
Geraghty's floated pass put Ashton over, although the fly-half failed with the tough conversion.
Gopperth got the Falcons on the board with a 15th-minute penalty, but Geraghty, looking to bounce back after losing his place in the England side that faced New Zealand, replied in kind seconds later.
The hosts were on top throughout much of the first half though and finally got the breakthrough after turning down the chance to go for goal on three occasions.
A lovely line of running from James Hudson saw the second row offload to put Biggs over in the corner after some fine build-up. Gopperth hit the post with the conversion to leave the score 8-8 at the break.
But Saints took control after the break when prop Soane Tonga'uiha offloaded to allow Ashton to sprint over for his second try of the evening after 50 minutes.
Geraghty added the conversion, and bagged three further penalties to seal the win.
A miserable second half for Newcastle was compounded when Micky Young was stretchered off after prolonged treatment in the final minute, and when play restarted Geraghty's cross-kick gave Ashton the simplest of finishes to complete his treble.
Northampton boss Jim Mallinder:
"We made a few mistakes in the first half but we improved in the second half. We tried to play a little too much but we got on top and our scrum was strong, we looked after the ball well and scored some good tries."
"(Ashton) is improving all the time and he had a good all-round game.
"Not just his try-scoring, but his kicking and defence and he is working very hard at improving."
Newcastle director of rugby Steve Bates: "We allowed them in for a fairly ordinary score early in the second half and they got their noses in front and we were left chasing the game.
"That gave them a bit of confidence and that was the turning point.
"The key is we have had two really tough games in five days.
"Travelling to Irish and back didn't give us a great deal of time to prepare and with a small squad we have to look at how we deal with those turnarounds, it's really difficult. In the second half that may well have been a factor."
Newcastle: Amesbury; Williams, Vickerman, Tu'ipulotu, Biggs; Gopperth, Young; Golding, Vickers, Hayman, Hudson, Sorenson, Swinson, Welch, Balding. Replacements: Bobo for Williams (68), Miller for Vickerman (71), Charlton for Young (79), Thompson for Vickers (71), Williamson for Sorenson (53), Afu for Balding (41). Not Used: Ward, Ovens.
Sin Bin: Young (53).
Northampton: Foden; Ashton, Clarke, Downey, Ansbro; Geraghty, Dickson; Tonga'uiha, Hartley, Bonorino, Lawes, Kruger, Dowson, Best, Wilson. Replacements: Murray for Bonorino (41), Day for Kruger (59), S Gray for Best (68). Not Used: Sharman, Dreyer, Dickens, Myler, Mayor.
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