In a frantic first half where both sides looked to constantly keep the ball alive, Saints replied to two Exiles tries through Fraser Dingwall and scrum-half Mitchell’s double. Dan Biggar also slotted three kicks to open up a 25-14 lead at the break.
It was more of the same once the players came back out, as Sleightholme scored two of his own to go with a Piers Francis effort, with Chris Boyd’s charges securing a bonus-point win at Franklin’s Gardens.
Irish opened the scoring in the ninth minute, as Nick Phipps dummied his way through a gap inside the 22 and Jackson converted for 7-0.
But almost immediately, Saints had levelled. Offloads from Mikey Haywood and Paul Hill allowed Mitchell to find Dan Biggar scything back on a hard inside line, one that saw him cut untouched through the Irish defence. With Dingwall running on the outside shoulder, it was an easy draw and give to send the centre under the sticks.
A Lewis Ludlam breakdown steal in midfield quickly had Saints back on the front foot, and the reward came when the visitors strayed offside. Biggar slotted his second kick of the evening from close to halfway.
A back and forth first quarter then saw Ollie Hassell-Collins breaking through the line off an inside ball from Terrence Hepetema, handing the visitors the lead after 20 minutes.
Saints continued to threaten with their offloading game, as Hill once again showed off his skillset to open up a hole. After Tom Collins had broke into the 22, Mitchell wasn’t held after sniping around the edge, allowing him to smartly return to his feet and ground next to the posts. Biggar had another simple conversion to make it 17-14.
Straight from the kick-off after conceding, Irish’s night got that more tricky when Ben Loader was sent to the bin for taking out Nick Isiekwe in the air.
Northampton immediately went back on the attack, but their first effort at a depleted Irish line was halted when referee Wayne Barnes collided with Collins as he looked for an inside pop.
Off the resulting scrum, the understaffed Irish defence was exploited as Mitchell again showed off his eye for a gap. Carrying from the base down what was Loader’s wing, he brilliantly found the space before speeding off past the cover for a long-range score.
With half-time fast approaching, Biggar would have been under the sticks had a Dingwall offload gone to hand, but advantage was being played. The Welshman tapped over a penalty from straight in front to leave the score at 25-14 at the break.
Saints started the second half brightly as Sleightholme again was close to getting on the end of a kick into the 22, but it was the visitors who notched the first score. James Stokes initially took a good angle to break close to the line, before Albert Tuisue crashed over from short range.
Sleightholme came close again when a Mitchell short pop sucked in the wide defence, but with a clear run to the line, he could only watch as Biggar’s pass was too high over his head and out of play.
The respite was brief for the visitors. First Dave Ribbans was held up after a clever lineout ball off the top, but from the scrum that followed, Sleightholme finally got his score – and Saints’ bonus point try – once the Irish defence was sucked in.
Another Ludlam breakdown penalty allowed Saints to turn the screw. Once Biggar had kicked into the corner, his wrap around and ball to the wide channel saw Francis speed off into the corner. Biggar matched his assist with a pin-point touchline conversion to leave the score at 37-19 heading into the final quarter.
That try saw the introduction of Tom Wood, with the flanker coming off the bench to make his 200th Premiership appearance.
With ten minutes to go, Sleightholme secured his double. Running at full-tilt after a Rory Hutchinson kick in behind, he showed off his footwork with a deft touch over the line before diving for the score.
A Ben Loader effort did secure Irish a bonus point of their own, while Biggar ended the contest in the bin after a deliberate knock-on. Neither side added to the scoreline as Northampton wrapped up an impressive victory ahead of next week’s derby trip to Leicester Tigers.