Tommy Makinson's 12-point haul helped St Helens ease to a 44-12 win over Castleford at Langtree Park.
Anthony Laffranchi, Paul Wellens, Makinson and Chris Flannery all crossed in a one-sided first-half, in which Cas replied only through Paul Jackson.
Saints then ran in four more tries after the interval though Makinson, young centres Gary Wheeler and Adam Swift and scrum-half Jonny Lomax.
Cas got a second try from Steve Snitch, Danny Orr again adding the extras.
Makinson landed two of his four kicks at goal before the break, while Wheeler kicked four from four.
Cas, who have now lost their last nine meetings with Saints, were without the suspended Jamie Ellis, while Ben Johnston was playing only his second game after making his debut in last week's heavy defeat by London Broncos.
Saints were without Michael Shenton, who missed the chance to face his old club, where he will return next season, because of an ankle injury.
Winger Ade Gardner was expected to return after being out since 9 April with an eye injury but he was kept out by Swift, who came in to form a new centre partnership with Wheeler.
Although Saints had lost their last two matches, any hopes that Cas boss Ian Millward had of making a winning return to his old club were dashed by half-time.
Saints then added four more tries after the break, all converted by Wheeler, the pick of them a length-of-the-field effort by Makinson after collecting a Richard Owen kick.
And a fifth successive defeat, coupled with London Broncos' shock thrashing of Warrington, now leaves 13th-placed Castleford in real danger of a first Super League wooden spoon since 2008.
VIEW FROM THE DRESSING ROOM
St Helens acting boss Mike Rush:
"Paul Wellens was my star man. He scored a try, made another for Tommy Makinson with a long pass and led from the front.
"Tommy was excellent too. Sometimes young players need a kick up the backside and he did well.
"Defensively it was a lot better and we only conceded two tries. Their first frustrated me a little bit but overall I have to be happy."
Castleford coach Ian Millward:
"We were really competitive in the first half but our completion rate went down from 70% to 50%.
"Saints defended really well. They are a top-three team and played better than they have in recent weeks.
"But I can't fault our effort and commitment. We had seven players out and three gone and we are not a big enough club to have that many players out."
St Helens: Wellens; Makinson, Swift, Wheeler, Meli; Hohaia, Lomax; Perry, Roby, Laffranchi, Soliola, Flannery, Puletua.
Replacements: McCarthy-Scarsbrook, Flanagan, Clough, Dixon.
Castleford: Owen; Youngquest, Snitch, Thompson, Griffin; Orr, Johnson; Emmitt, Hudson, Huby, Millington, Jones, Mitchell.
Replacements: Milner, Jackson, Holmes, Massey.
Referee: George Stokes (RFL).