Much of the focus was on returning star Leon Pryce, but it was 20-year-old Foster who stole the show with three tries and eight goals against the in-form Dragons.
Pryce came on to a rousing reception when he was introduced off the bench on the hour mark.
But Saints eventually pulled clear in spectacular fashion when they ran in three tries in the last eight minutes to produce a lopsided scoreline.
St Helens boss Royce Simmons said: “We let in some rather soft tries where they didn’t have to build pressure, and that was the part I was disappointed with, but our ball control went in the right direction.”
He added: “Leon’s experience is going to be very valuable for the rest of the year, but our other halves are also doing a tremendous job for us.”
On star man Foster, Simmons reflected: “Jamie’s goal-kicking was really good. He doesn’t miss too many, and he’s scoring some tries as well. He’s a good finisher, but you’ve got to give credit to Francis Meli too on a lot of Jamie’s tries.”
Foster had needed only five minutes to get Saints off the mark, benefiting from Meli’s offload after play had been spread from right to left through a succession of sweeping passes.
Menzies’ first try was all that Catalan had to show for their first half endeavour, with Meli bouncing off a stunned defender to edge Saints back in front before Foster landed a penalty to establish an eight-point buffer.
Foster’s second try was arguably his best, racing 50 metres after picking up a loose ball on halfway, but Vaccari, Menzies and Greenshields all crossed before the hour to swing the momentum in the Dragons’ favour.
They looked favourites to claim the points at that stage, but their late collapse left coach Trent Robinson fuming.
He said: “The game was obviously closer than the final scoreline, but we deserved what we got in the end.
“I thought we were better than what we saw tonight. It’s not about being third or fourth in the table – there’s an ethic you set the team and we let ourselves down in some areas.”