Williams also came up with a first-half drop-goal that gave Wire the edge at the break.
Saints’ first-half points came from a Konrad Hurrell try, improved by Jon Bennison, who scored their only points after the break with a penalty.
It was Wire’s start to the second period that won them the game as Saints were wrecked by two quickfire tries.
The first was a stunning one-hand finish in the left corner from Ashton, one of the great tries by any winger as, with almost the whole of his body the wrong side of the touchline, he snaked out his left arm and somehow kept control of the ball to touch it down with his fingertips.
Then came Wire’s third try from Wrench, also converted by Thewlis, before front-row forward Harrison crashed over to make it safe and Matt Dufty jinked through to set up man-of-the-match Williams for the final score.
St Helens: Welsby; Makinson, Hurrell, Blake, Bennison; Lomax, Dodd; Walmsley, Clark, Delaney, Sironen, Batchelor, Knowles.
Interchanges: Mata’utia, Mbye, Bell, Whitley.
Warrington: Dufty; J Thewlis, King, Wrench, Ashton; Williams, Hayes; Harrison, Walker, Philbin, Nicholson, Fitzgibbon, Crowther.
Interchanges: Bullock, Holroyd, Powell, Wood.
Referee: Jack Smith.
