Premiership champions Harlequins proved their credentials with an impressive victory over Northampton at Franklin's Gardens to stay top of the table.
A cagey first half saw Quins fly-half Nick Evans edge the battle from the kicking tee with Stephen Myler.
Myler levelled the scores on the hour with Quins' James Johnston sin-binned.
But Evans landed nine points in a 10-minute spell and, despite Ryan Lamb's late penalty, Evans's final shot at goal denied the hosts a bonus point.
With the regular Premiership campaign reaching its mid-way point Harlequins proved last season's title was no flash in the pan as they displayed a masterful adaptation of wet-weather rugby on the ground where they were pummelled 24-3 in the corresponding fixture 11 months ago.
Quins learned from that experience to emerge narrow 25-23 winners of last season's play-off semi-final with the Saints, on the way to domestic glory, and they illustrated the same aptitude for outfoxing their opponents again.
Johnston spearheaded a pummelling of the Saints scrummage on four minutes that allowed Evans to put Quins ahead early on.
The former All Black then threatened with an incisive line from deep before Samu Manoa charged down the Kiwi's clearance kick as chances were fashioned at either end in an entertaining opening quarter of an hour.
Myler levelled the score on 17 minutes, shortly after Evans had pulled a long-range attempt wide, but Ben Foden had the crowd on their feet when he powered his way over to round off a snappy Saints move.
But much to the home fans' dismay referee Wayne Barnes disallowed the try when he judged George Pisi's pat-pass to his full-back to be forward.
Myler missed a straightforward shot and, when Tom Wood was called offside guarding at the ruck, Evans re-established the visitors' three-point lead.
The rain, which had stopped prior to kick-off, returned to blight the handling and errors punctuated the game throughout.
Saints emerged after the break 6-3 down and almost fell further behind when England duo Mike Brown and Chris Robshaw combined to put the former England eight Nick Easter clear.
The big man charged up field and chipped over the advancing Foden only to be beaten to the ball by Saints' number 15.
Johnston then made a break of his own, before being hauled down short of the line, and, when Paul Doran Jones tried to pull Danny Care into the resulting ruck, Evans had a simple shot at goal.
The kick was pushed wide but, with Quins' forwards in the ascendency, the visitors exerted sustained pressure until Johnston saw yellow for not rolling away.
The numerical advantage allowed Myler the chance to level the scores again but Foden and Wood then gave away quick penalties, which Evans converted, and Quins had a six-point lead as Johnston returned.
Evans made it 15-9 but Saints worked their way back up the field where Tom Williams handed Lamb three points when he threw away the ball to prevent a quick line-out.
With the game drawing to a close the hosts found themselves pressure again and conceded a further penalty in front of the posts which Evans made no mistake with.
VIEWS FROM THE DRESSING ROOMS
Northampton Saints director of rugby Jim Mallinder told BBC Radio Northampton:
"It was a really tight game. The conditions weren't there for running rugby.
"It was close up to 60 minutes. We had a little momentum when they went down to 14 men and that's when we should've put more pressure on them. We made a couple of stupid mistakes.
"Quins are top of the table because they're a very good side. I thought Mike Brown at full-back was outstanding in difficult conditions.
"I don't know if Ben Foden's (disallowed) try was a forward pass or not, that's irrelevant, we've got the technology and we should use it."
Harlequins director of rugby Conor O'Shea:
"It was a great team performance. Nick [Easter] will keep knocking on the [England] door, and he is in incredible shape.
"I just saw in our senior guys through the week a mentality that they wanted to come here and make a statement.
"That is 14 wins out of 17 in all competitions and we are playing poorly I am being told."
Foden; K Pisi, G Pisi, May, Elliott; Myler, Dickson; Tonga'uiha, Haywood, Doran-Jones, Manoa, Lawes, Wood, Dowson, van Velze.
Waldouck for May (57), Lamb for Myler (72), Roberts for Dickson (72), A. Waller for Tonga'uiha (62), Mujati for Doran-Jones (42), Sorenson for Lawes (68).
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.