Substitute forward Alex Walmsley grabbed two tries as St Helens overcame a 12-man Salford outfit 30-4 to effectively seal their place in the Super League semi-finals.
A third successive victory snuffed out Wakefield's lingering hopes of a top-four finish and lifted Saints up to third place with a healthy points difference, leaving Wigan likely needing to win by an improbable 90-point margin in their final Super 8s fixture.
That comes at Wakefield on Saturday and by then, if Hull have taken at least a point from Castleford on Friday, their season will be effectively over.
Salford battled hard despite the 37th-minute dismissal of forward Ryan Lannon for a high and late tackle but finish a season that promised so much with a ninth defeat in their last 10 matches.
The Red Devils made the better start, though, with former New Zealand Test winger Manu Vatuvei catching the eye with a strong burst before fullback Niall Evalds cut through for the game's opening try straight from a well-worked scrum set move.
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But the home side paid the penalty for a series of handling errors from their slipshod threequarters which enabled St Helens to build up a head of steam.
Pressure on the visitors' line told on 16 minutes when Saints' marquee Australian fullback Ben Barba slipped the tackle of Kris Welham to give centre Mark Percival a clear run to the line for an equalising score.
The turning point came 10 minutes before half-time when Vatuvei was denied a try by video referee Phil Bentham for a knock-on in the build-up to a smart attacking move and a minute later prop Walmsley crashed over for his first try.
