Picamoles scored the first and set up the second, for replacement scrum-half Tom Kessell, as Saints bounced back from last Saturday’s 41-7 evisceration at Castres.
But Gloucester had got the home supporters’ nerves jangling when they took a 20-16 lead 20 minutes from time.
It took a classy Picamoles offload to set Kessell free and with Stephen Myler, who landed all five of his kicks at goal, making the conversion, Saints had a three-point lead.
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And despite some late Gloucester pressure, Jim Mallinder’s men were able to hold out for their third win in seven Aviva Premiership matches this season.
Saints had needed a big response after the Castres calamity, but with fans still flooding into the Gardens, Gloucester started the game on the front foot, bossing the early territory.
Saints had conceded an early penalty, which Gloucester kicked to the corner, but they went for goal with another. However, Greig Laidlaw sent his effort wide.
George North thought he had scored soon after, but after touching down, the Wales wing realised referee Tom Foley deemed Harry Mallinder’s pass forward.
Laidlaw then missed another penalty chance at the other end as a game that really needed a catalyst continued to meander in the middle of the field.
Both sides were searching for some inspiration and Saints found it in the form of a man who has been a beacon of light amid the early-season gloom, Picamoles.
The French star pushed his way over and Myler converted to make it a 7-0 lead after 26 minutes.
Myler was soon adding a penalty to increase the advantage, but it was third time lucky for Laidlaw at the other end as he cancelled the Saints kick out.
But a scrum penalty saw Saints quickly restore their 10-point lead through Myler’s assured boot and the home team headed in at half-time 13-3 up.
Gloucester were to score soon after the interval though as Saints’ defence, which had been strong, melted away and flanker Jacob Rowan had an easy run-in.
Laidlaw converted to cut the gap to just three points and suddenly the pre-match nervousness had returned to the Gardens.
And the atmosphere was even more fraught a few minutes later as Gloucester again found their way over out wide, with Charlie Sharples scoring.
Laidlaw’s conversion was accurate and the away side led by four points with 20 minutes to go at an anxious Gardens.
Ben Foden continued to battle for Saints and again opened Gloucester up, but Rory Hutchinson was eventually well stopped as the home team huffed and puffed.
And they eventually blew the door down as Picamoles again played a huge part, offloading for Kessell to score.
Myler converted and the feeling of relief was palpable, but James Hook was soon lining up a long range penalty in a bid to level the scores.
However, Hook’s ambitious attempt fell short and Saints were able to clear their lines with three minutes to go.
Still Gloucester came thoughh, and Saints had to defend for their lives as they eventually won a penalty, to the delight of the home fans, who celebrated a vital victory.
Saints: Foden; Wilson, G Pisi (Tuala 78), Mallinder (Hutchinson 59), North; Myler, Dickson (Kessell 62); A Waller (E Waller 67), Haywood (Hartley 57), Brookes (Hill 59); Paterson (Ratuniyarawa 59), Day; Wood (c), Clark (Gibson 9), Picamoles.
Gloucester: Hook; Sharples, Scott, Atkinson (Burns 70), May; Twelvetrees, Laidlaw (c); McAllister (Orr 64), Hibbard (Matu’u 70), Afoa; Savage, Galarza; Moriarty (Kvesic 64), Rowan, Morgan.
Referee: Tom Foley