A week after surrendering the Challenge Cup with their semi-final defeat by Huddersfield, Saints' grip on top spot in Super League was loosened by Hull Kingston Rovers.
The Robins gave a concise seminar in the second half on how to use the conditions at a blustery Craven Park. Whereas Saints had squandered the advantage of the strong wind at their backs by persistently kicking too deep, Rovers exploited it cleverly to sustain pressure and score three tries in the 15 minutes after the break.
Saints had their excuses for the fourth defeat in their last seven games. They were down to their fourth-choice scrum-half, the 19-year-old Jamie Ellis, whose contribution included putting James Graham over for the game's first try.
Rovers initially looked off-colour, with their best chance going to waste when Kris Welham took Ben Galea's long pass and failed to move it on to his wingman. Welham did much better on the stroke of half-time, swooping on a loose ball and going 40 metres for the converted try that put his side ahead.
After the break, they were a team transformed. Michael Dobson's kick forced a drop-out, from which they attacked down the right for Jake Webster to score from Ben Cockayne's pass. Cockayne was involved again when Rovers continued the attack direct from the kick-off, supplying the final pass from which Daniel Fitzhenry surged over.
His second came when Chev Walker was halted on the line and Fitzhenry, who has been told that there is probably no contract for him when the overseas quota tightens next season, spotted a gap from dummy half.
The rampaging Rovers also had a couple of efforts disallowed. Had they stood, Saints' advantage over Leeds in points difference could have disappeared. As it was, they held out until a minute from time, when they got into a tangle on their left flank and Peter Fox touched down the loose ball.
Saints got one back from the last play, Ade Gardner catching a neat kick from the promising Ellis. It was a weekend, however, during which the balance of power had shifted.
"We've no buffer anymore," admitted Saints coach, Mick Potter. "We'll just have to keep on winning."
For Rovers, a first double over Saints since 1981 is exactly the sort of confidence-booster you want to carry into the play-offs.
Hull KR: Briscoe; Fox, Webster, Welham, Colbon; Cooke,Dobson; Fozzard, Fitzhenry, Vella, Newton, Galea, Cockayne. Substitutes used: Walker, Wheeldon, Netherton, I'anson.
St Helens: Wellens; Gardner, Gidley, Gilmour, Meli; Pryce, Ellis; Graham, Roby, Puletua, Wilkin, Flannery, Dixon.
Substitutes used: Hargreaves, Clough, Ashurst, Wheeler.
Referee: S Ganson (St Helens).