Tom Guest clinched victory for Harlequins with a try from close-range four minutes from time to beat a stubborn Newcastle in this Aviva Premiership Rugby clash at the Twickenham Stoop.
The hosts had led just 9-6 at the break with fly-half Nick Evans kicking three penalties and opposite number Jimmy Gopperth landing two for Newcastle.
But a penalty try extended the Quins' lead and, although two more penalties kept Newcastle in the game, Guest's try put the home side out of sight.
Quins were looking to build on last week's emphatic home win over Exeter while Newcastle were anxious to recover from their hammering at the hands of London Irish.
But Harlequins took control from the first whistle, and they were ahead on five minutes when Evans calmly stroked over the game's first penalty.
Quins continued to impress, maintaining their initiative at pace, forcing Newcastle to play and defend on the back foot.
Despite the rain, which began to fall minutes before the match, Quins opted for a handling game which stretched their visitors at the breakdown and left them struggling for possession.
And it was evident from the first scrum that 20 year-old loosehead prop Joe Marler, who made his first Aviva Premiership Rugby start last weekend, was bossing Tim Ryan in a manner that spelled danger for Newcastle.
For all that, Quins managed to fall foul of referee Chris White on 15 minutes, infringing at the breakdown and presenting Gopperth with a penalty opportunity from 40 metres that he accepted, despite slipping during his run-up.
That lifted Newcastle considerably, and it was the turn of their hosts to face last-ditch defence on their line. Jeremy Manning hesitated when he could have stretched out an arm and touched down before Gopperth wasted the opportunity with an ambitious cross-kick that went dead wide on the left.
Gopperth then had a chance to give Newcastle the lead on 20 minutes, but his penalty from the left wing missed the far post.
Harlequins quickly regained control, however, drove up field and earned a penalty on 24 minutes which Evans drilled over to regain the lead.
And when Newcastle gained possession shortly after, Quins battered into them to force a turnover, and had George Lowe held a clever cross-chip from Evans he could well have been in.
Despite their superiority, Quins failed to convert it into points which meant Newcastle remained only one score adrift – and Gopperth levelled matters with a huge kick from close to halfway after Quins pulled down a maul.
This was followed by another period of Quins pressure that finally paid dividends when Evans rammed over a penalty two minutes from the break after Chris Pilgrim lost patience and pounced on Danny Care before the ball came out of a ruck.
Quins ripped through Newcastle in some style straight from the restart as Mike Brown and Care engineered a chance that petered out on the line when Pilgrim managed to get under the ball on his line.
But Quins kept pressing, winning three penalties at scrum time which saw Falcons prop Jon Golding sin-binned – having only been on since half-time.
When a fourth scrum was crushed White had no option but to award a penalty try, and Evans added the conversion.
Gopperth remained Newcastle's best hope of staying in touch, and another long-range penalty on 49 minutes cut the deficit.
Quins then conceded a stupid penalty when Marler slapped the ball out of Pilgrim's hand and Gopperth punished him with another three points.
This was Newcastle's most assured period and it was Quins who found it tough to get hands on the ball going into the final quarter.
But Quins held firm and avoided any more gifts near their posts, with Guest's try sealing the win.