Murley did also complete his double before full-time, but it was nowhere near enough as Quins suffered a 40-22 defeat.
Marcus Smith put the away side ahead with a penalty, but that was all they had to cheer about early on as Northampton took control.
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Rory Hutchinson’s sublime pass set up Naiyaravoro out wide and the powerhouse wing was far too strong for the Quins defence, shoving his way over the line.
James Grayson could not land the conversion from the touchline, but he did better with another effort soon after as David Ribbans did some fine work in the build-up to a Harrison try.
Grayson’s successful penalty made it 15-3 and Harlequins were floundering as Saints continued to march forward.
Naiyaravoro soon picked up a pass out wide and used his strength once more to barge a defender away before diving over in the corner.
Grayson converted and Northampton were just one try from the bonus point – less than half an hour into the contest.
It took them a further 11 minutes to get it as hooker Haywood, making his first start since last November, got the ball down from the back of a dominant lineout drive.
Grayson missed the conversion but Northampton were in cruise control at 27-3 up.
Quins threatened to respond late in the half as full-back Aaron Morris was stopped at the last by Andy Symons.
Murley was able to reduce the deficit before half-time though as the replacement found space and used it well.
Smith missed the conversion at the end of what was a tough half for his team, but they emerged with purpose in the second period, putting pressure on.
Northampton eventually paid the price as a quick tap penalty allowed Robshaw to go over, with replacement Brett Herron converting.
But Grayson landed a drop goal to ensure Northampton would lead by 15 points with 20 minutes to go.
And the fly-half soon slotted a penalty before a lovely flowing move saw Hutchinson, Fraser Dingwall and Grayson all combine before Harrison scored his second in the corner.
Murley had the final say with his second effort of the night which was again converted by Herron.
Saints lock Alex Coles saw yellow before the end, but Northampton had done more than enough to win it.
– Press Association
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