The heavy rain which set in during the hour preceding kick off and continued unrelentingly throughout the 80 minutes meant that anyone who was expecting a feast of expansive rugby was always going to be disappointed.
In such conditions results inevitably depend on who comes out on top up front and in the battle of the kickers, and in both areas Saints were worth the final result.
After conceding an early try, the pack got on top in most facets of their game, while Ryan Lamb continued his recent good form with his boot to earn himself the Travis Perkins man of the match award, landing a drop-goal, two conversions and a pair of penalties as well as setting up Ken Pisi's first half try which took their team seven points clear going into half-time.
Having gone ahead Saints kept themselves clear with Lamb's two second half penalties, but with just six minutes on the clock they had to regroup having gone behind to an early penalty try.
London Welsh had dominated the early possession and when their forwards put in a massive effort to drive a maul fully 20 metres towards the uprights it was relatively little surprise that when the mass of bodies collapsed referee David Rose opted to give the visitors the score.
Gordon Ross landed the conversion, to which he added a penalty six minutes later, and to add ignominy to insult GJ Van Velze was sent for a 10-minute spell on the sidelines.
Saints nevertheless shrugged off the South African's temporary absence to put themselves in the position from which Lamb slotted his drop goal, and then when Van Velze returned they turned on the power at a scrum and subsequent lineout in some style.
Franck Montanella became the second player to see yellow for pulling a maul down, and when Saints got the nudge on at three successive scrums close to the Welsh line it was only a matter of time before a penalty try was awarded.
It wasn't long before Saints were back in the red zone, but this time they were thwarted by some excellent scrummaging from Welsh, twice with seven men and the third back to the full eight.
The relief and joy shown by the visitors' team and bench was palpable and obvious. However their cheers turned sour just after the half-hour when wing Dan Caprice became the third player of the day to be sent to the sin bin, this time for taking Jamie Elliott out in the air.
Again Saints took advantage of the extra man, putting the ball through the hands well to make metres down Caprice's now empty wing. Welsh's defence was struggling to get back in line and when Lamb sent a pin-point crosskick to the unmarked Ken Pisi all the Samoan had to do was slide over for the score.
Lamb belied the wind and rain to convert from the touchline, and when the fly half added a penalty four minutes after the re-start he put his team two scores clear for the first time.
However Welsh had come out of the dressing rooms rejuvenated, and got themselves back in touch with another Ross success from the tee. They had another two shots at the uprights from Tom Arscott, but the best thing that could be said about those 50-metre-plus efforts was that they put Welsh a few metres upfield following the drop-outs.
Saints were also letting Welsh off the hook with some lineouts that saw the ball rebound agonisingly off fingertips or from the deck. But when Van Velze took a Welsh throw cleanly it provided the impetus for Saints to maul upfield and win two penalties in quick succession.
Lamb converted the second, and with the 10-point cushion he started to take advantage of the gaps which were appearing in the visitors' defence. The runs were asking questions, but it was the tactical kicking which forced Welsh to play from deep within their own territory.
And while they had the last say on the scoreboard with Ross's penalty eight minutes from time all this did was earn the visitors a bonus point and Saints were able to run the clock down in some comfort.
6mins SAINTS Yellow card Van Velze
6mins WELSH Try Penalty Con Ross 0-7
9mins SAINTS Drop goal Lamb 3-7
12mins WELSH Pen Ross 3-10
15mins WELSH Miss pen Ross
20mins WELSH Yellow card Montanella
25mins SAINTS Try Penalty Con Lamb 10-10
33mins WELSH Yellow card Caprice
35mins SAINTS Try Pisi Con Lamb 17-10
HALF-TIME SAINTS 17 L WELSH 10
44mins SAINTS Pen Lamb 20-10
47mins WELSH Miss pen Arscott
54mins WELSH Pen Ross 20-13
56mins WELSH Miss pen Arscott
64mins SAINTS Pen Lamb 23-13
72mins WELSH Pen Ross 23-16
FULL-TIME SAINTS 23 L WELSH 16