Saints got off to an uncomfortable start after changing their line-up before the game when winger Francis Meli was withdrawn before kick-off with a pulled muscle.
He was replaced by youngster Dean McGilvray who had already played 80 minutes in the pre-match academy curtain raiser.
Saints got off to the worst possible start when Kiwi centre Willie Talau fluffed a Sam Obst kick to allow Sean Gleeson to nip in and grab a touchdown after only four minutes.
Saints' response was immediate with fine play by Paul Sculthorpe and Ade Gardner fashioning the opportunity for Matt Gidley to cancel that out.
Sculthorpe added the extras and then Saints took the lead that they would not relinquish on 16 minutes when some patient handling worked the space for Leon Pryce to dart over from 10 metres out for a converted try.
A Jamie Rooney penalty cut the deficit to four points as the conditions deteriorated due to the driving rain.
But after hitting a sticky patch Saints nudged further ahead when Matty Smith and Gidley combined to send Gardner streaking in at the corner to make it 16-8 at the break.
It took Saints 11 minutes to open their second-half account with the champions finding it difficult to break down the stubborn Trinity defence.
A speedy burst from Gidley pierced the line to open up a 12-point lead and kill off their resistance.
Wellens then polished off some fine work from Pryce, Gidley and Smith for his first touchdown.
He then added his second to keep up his prolific scoring run.
The latter came after Trinity were temporarily down to 12 men when David March was sin-binned for a late tackle.
The visitors had the last word when an up and under was fumbled to allow Oliver Elima to touch down.
St Helens (16) 34. Tries: Gidley 2, Pryce, Gardner, Wellens 2. Goals: Sculthorpe 5.
Wakefield Trinity WIldcats (8) 14. Tries: Gleeson, Elima. Goals: Rooney 3.
St Helens: Wellens, Gardner, Talau, Gidley, McGilvray, Smith, Fozzard, Cunningham, Cayless, Wilkin, Sculthorpe, Hargreaves, Roby. Replacements: Graham, Clough, Fa'asavalu, Pryce.
Wakefield Trinity Wildcats: Rooney, Pryce, Gleeson, Demetriou, White, Obst, P. March, Moore, D. March, MacGillivray, Catic, Ferres, Henderson. Replacements: Jeffries, Bibey, Golden, Elima.
Referee: G Hewer