Tries from Bruce Reihana, Juandre Kruger and Soane Tonga'uiha gave Saints a sniff of a bonus point with Stephen Myler kicking three penalties. Quins' two second half tries came from Josh Drauniniu.
Saints took the lead through Reihana's try after
five minutes that really should have been cleared up by England winger David Strettle.
Quins fumbled on halfway and Saints quickly moved the ball to the opposite wing where Jon Clarke decided to chip over the cover.
Strettle won the foot race, but the ball bobbled through his hands and Reihana picked up to dive into the corner. Myler missed the conversion to leave Saints 5-0 in front.
Quins come straight back and former Saint James Percival was held up over the line after Evans kicked a penalty into the corner.
From the 5m scrum Karl Dickson arched for the line, but his brother Lee hauled him down and when the Quins forwards tried to smash over there was a knock-on.
Phil Dowson had a great chance to score from a tap penalty 10m out with half the Quins side still up field after being penalised for offside, but he failed to pass and the chance was snuffled out.
On 19 minutes, though, Myler extended Saints' lead by using the strong wind to land a 52m penalty.
Saints' backs looked in confident mood, with a sweeping move that got the home side within 5m. Then a break from Chris Ashton off a lineout brought a penalty as Roger Wilson was held back.
While Myler lined up his 35m shot, there was a loud cheer as Bloodgate whistleblower Tom Williams received treatment, hopefully not involving a blood capsule. Myler converted the penalty to make it 11-0.
But on 34 minutes Quins were given a way back into the match when Best was sin-binned for a dangerous tackle, when he bodychecked a Harlequin with a loud slap. Nick Evans kicked the penalty to make it 11-3.
Quins should have followed that up with a try when ex-Saint Nils Mordt burst through off a 40m lineout and sent Mike Brown hurtling down the left wing, but his offload 5m out went straight into touch.
Moments later Quins looked to have made the extra man count when Williams scooted into the left corner, but it was brought back for a forward pass.
Saints were let off again on half-time when the home scrum stood up. It gave Evans an easy penalty, but it was reversed thanks to an off-the-ball misdemeanour from Percival.
Saints turned over the second half kick-off and quickly won a penalty, which Myler slammed over from 35m to make it 14-3.
Quins did the same and piled on the pressure, moving 14-man Saints left and right, but Neil McMillan was stopped just short and Best returned.
Saints survived more pressure and there was rapturous applause as now England lock Courtney Lawes took the field after 48 minutes. And there was an even bigger cheer when Euan Murray came on for his first action of the season after his bad injury on the Lions tour.
The home side struck again on 59 minutes when Myler sent Soane Tonga'uiha through a large hole and he passed to Kruger to touch down. Myler missed the conversion to leave Saints 19-3 ahead.
With 11 minutes to go Harlequins finally got the try they deserved when Evans smashed through Myler off a 30m lineout to leave replacement wing Drauniniu with an easy finish in the corner. Evans converted to make it 19-10.
Tonga'uiha sealed his man of the match award by bulldozing over from 5m after a nifty bit of play by Alan Dickens down the blindside. Myler landed the touchline conversion.
With a minute left Saints went for the bonus point, but instead Drauniniu intercepted on his 22 to speed home for this second try, which Brown converted.
Att: 13,040
Saints - Foden; Ashton, Clarke, Downey, Reihana; Myler, Dickson; Tonga'uiha, Sharman, Bonorino; Day, Kruger; Dowson (capt), Best, Wilson
Reps - Gray, Dreyer, Murray, Lawes, Gray, Dickens, Everitt, Ansbro
Harlequins - Brown; Strettle, Lowe, Mordt, Williams; Evans, Dickson; Jones, Fuga; Andress, Percival; Robson (capt), McMillan, Guest
Reps - Brooker, Croall, Lambert, Stevenson, York, So'oialo, Clegg, Draunin
