A try double by returning winger Ross Adair helped the Reds to a narrow cup success that took them ahead of opponents Scottish in pool 1 of the B&I.
The 23-19 win completed back-to-back wins over the Exiles, who had led 7-10 at half-time and enjoyed a larger six-point margin (13-19) on the hour prior to the Reds battling back to take the points.
Fly-half George Cullen, taking up kicking duties for the visitors after the late withdrawal of Peter Lydon, gave his side the lead with a straightforward 9th-minute penalty, but then in their first meaningful attack the Reds worked the ball wide to Adair who surged across for a try, with Sam Katz converting from the touchline.
Jersey had the chance to seize control of the match soon afterwards, but although Exiles' hooker George Turner was sin-binned for dragging down a maul, claims for a penalty try went unheeded and a subsequent attacking opportunity came to nothing as lineout possession was lost.
The visitors survived Turner's absence unscathed, and were then able to score a try soon before the break. A series of forward drives set the platform, yielding a penalty advantage from the referee, and the Jason Harries wriggled through the middle to cross under the posts.
Cullen notched an early penalty after the break, but then Katz added two penalties of his own with the Reds deciding to take points when they were on offer rather than kicking for the corner.
The kickers then landed a further shot apiece to leave the score at 16-19 before the Reds charged forward, with Max Argyle's powerful run making crucial yards. Recycled possession came to Adair and the Ulsterman chipped delicately through and was awarded the touchdown, although the Exiles also claimed to have grounded the ball.
Another Katz conversion gave the hosts a four-point margin and although the fly-half missed a 78th-minute penalty, his first unsuccessful effort, the Exiles were unable to gain the field position to secure a winning score.
Jersey's win saw them go top of pool 1 ahead of the Saturday clash in Pontypridd between Cardiff Blues Select and Ulster 'A', and delighted Head Coach Harvey Biljon.
"People may think we won ugly but that was a terrific effort from the whole squad," he said. "There was some great impact from the subs and once again we were having to field three scrum-halves in the second half.
"We were trying to score tries in the first half, being brave in front of our home crowd, but then we had the positions from which to take some penalties after the break. After six or seven weeks out it was a great comeback from Ross Adair to get two tries - they were crucial scores."
Jersey return to Greene King IPA Championship action with an away trip to Bedford on Boxing Day, and will next be in action on home turf when Ealing Trailfinders visit for a Championship match on New Year's Day (k-o 2pm).
JERSEY REDS: Cuthbert (Dudley 42-52, 56); Watkins (Hardy h-t), Ma’afu, Davies, Adair; Katz, Fisilau; Woolmore (McCarthy 52), Macfarlane (Buckle 60), Armstrong (Tampin 47), Campbell, McKern (Kolo'ofa'i 68), Freeman (c), Doyle (Haining 52), Argyle.
LONDON SCOTTISH: Galbraith; Coombes, Fergusson, Kelly (Rath 78), Harries; Cullen, Hoadley; Harris (Shiells 56), Turner (YC 23), McQuillin (Cringle 56), Hunter Hill, Patrick, Bartle (c), Kenny, Ifereimi (Marley 47).
Not used: Koroi, Atkinson, Holland
REFEREE: Ben Blain (RFU); Assistants: Andy Watson, Ian Bibey
Man-of-the-match (as chosen by match sponsor Santander): Ross Adair (Jersey)
Half Time: 7-10
Tries: Adair 17, 69
Conversions: Katz 17, 49
Penalties: Katz 49, 51, 63
Try: Harries 38
Conversion: Cullen 38
Penalties: Cullen 9, 43, 54, 58
Why not get yourself a Hot Pot (Curry or Chilli served with rice) in the supporters marquee £8 per pot.