Outside half Stephen Jones pulled the strings perfectly from behind the scrum in a performance which had Davies claiming his star was playing some of the best rugby of his career.
After last week's encouraging team performance, Jones has warned Quins that the Welsh region are hoping to continue to rebuild their European credentials.
Jones said: "Although the Heineken Cup is over for us this season, our ambitions are to keep going forward as a side. We need to keep on gathering momentum and improving our performances.
"We have a tough game against Harlequins before refocusing on the Celtic competition, and, while it's all about performing well now, it is also important to secure points for the ERC European rankings for next year.
"As for the match on Saturday in London, when you see the Scarlets play the type of game that we played against Stade last weekend - and which we know we can do and have done in the past, though probably didn't do last year - I think we have the ability to win."
This weekend's Scarlets team sees scrum-half Lee Williams keep his place on the wing where he played last week due to back-three injuries. Ceiron Thomas remains at full-back and, on the bench, there are recalls for lock Scott MacLeod, centre Gavin Evans and full-back Morgan Stoddart.
Stephen Jones admitted that a home European defeat to Quins at Stradey Park in October had had a negative effect on the Scarlets' season.
He said: "Going back to our first game against the Quins earlier in the tournament we were outstanding in the first half and probably should have won a bonus point by half-time. But we didn't achieve that and the second half really knocked us. It took us a long time to recover so hopefully we'll see a full 80-minute performance this time.
"We did Quins a favour by beating Stade last weekend but it was always about us in that game and we would like to think we've re-established some European credentials."
It was the Scarlets' debut European win at their new home at Parc y Scarlets and Jones believes it will prove only the first of many.
"We seem to have built up something nice here in this stadium and it feels like home now. Winning here was definitely good for us, good for the fans and good for the future. We have to make sure people are keen to come here and if we keep playing like that there's no reason why we shouldn't continue winning.
"We've not given our fans much to cheer about in the last 18 months so we are pleased for them with this important result. From our perspective, things don't happen straight away so it's with moments like this victory in the Heineken Cup against a top team that you create more history for the club.
"Because not only are we are very happy with the victory, but also our performance was good. The challenge for us was to sustain the pressure for a full 80 minutes and we managed that.
"We probably showed more enthusiasm and hunger than them, the boys believed in themselves and were outstanding."
Wales flanker Dafydd Jones replaces the injured Johnathan Edwards, who broke his arm in the 31-17 win over Stade Français last Sunday, as the only enforced change in the Scarlets line-up.
Scarlets 15 Ceiron Thomas, 14 Darren Daniel, 13 Regan King, 12 Jonathan Davies, 11 Lee Williams, 10 Stephen Jones, 9 Martin Roberts; 1 Phil John, 2 Matthew Rees, 3 Deacon Manu, 4 Vernon Cooper, 5 Dominic Day, 6 Simon Easterby (c), 7 Dafydd Jones, 8 David Lyons.
Reps - 16 Ken Owens, 17 Iestyn Thomas, 18 Scott MacLeod, 19 Josh Turnbull, 20 Gavin Cattle, 21 Gavin Evans, 22 Morgan Stoddart.