Northampton pulled seven points clear of third-placed Bath in the Aviva Premiership table after securing an edgy 36-21 win over London Irish at Franklin's Gardens.
After 42 minutes the game looked over as Salesi Ma'afu scored Northampton's fourth try to make it 29-0, adding his score to two from Jamie Elliott and one from Kahn Fotuali'i.
But a series of calamitous errors saw Irish come back with three second-half tries from Shane Geraghty, Andrew Fenby and Jebb Sinclair.
It might have been four if the TMO had not scrubbed off Marland Yarde's 60-metre effort.
Instead Alex Waller added a fifth with the clock dead, which James Wilson converted to add to Stephen Myler's three conversions and a penalty.
Despite scoring no points in the first half, Irish - without skipper George Skivington, James O'Connor or Topsy Ojo - looked dangerous and spurned three gilt-edged chances.
Geraghty, who was welcomed back by a thunderous hit from George Pisi after just four minutes that saw him being sick on the pitch, was a constant threat.
But it was Northampton who opened the try-scoring on 13 minutes.
Fotuali'i's box-kick was deflected and it bounced into the arms of Elliott on the right touchline. He cut inside Alex Lewington from 25 metres out and, although the full-back got back to tackle the winger, his momentum took him under the posts.
There was some doubt he grounded it, but referee JP Doyle did not go to the TMO.
Fotuali'i claimed a bizarre second try for Saints when Tomas O'Leary's box-kick was partially charged down by Phil Dowson.
It flew high towards the left touchline, but bounced just inside, evading Yarde and North, but into the arms of the Saints scrum-half who scooted over unchallenged from just inside the Irish 22.
Five minutes later Ben Foden somehow shook off three Irish players and raced into the visiting 22, where some quick hands moved the ball to Elliott to score his second try.
Myler added the extras to make it 24-0 two minutes before the break and take him over the 1,000 Premiership points mark.
It took just 84 seconds of the second half for Saints to wrap up the bonus point when Luther Burrell broke through on halfway. Irish scrambled back but Ma'afu rumbled over from close range.
However, Northampton then conspired to let Irish back into the game.
Burrell bizarrely kicked on Fenby's grubber and the Irish winger won the race to dot under the posts for Geraghty to convert, then Tom Wood fumbled and Geraghty picked up the loose ball in his 22 to race home.
And when Alex Waller was sin-binned, Sinclair squirmed over for a third try converted by Geraghty to suddenly make it 29-21.
Yarde looked to have made it a one-point game when the winger raced home from 60 metres, but the TMO ruled Tom Homer's pass to him forward.
Instead, with the clock dead, a relieved Saints conjured up a fifth try for Waller.