Saints are one match away from what has become their customary place at Old Trafford after surprising a well-fancied Warrington side that must now try to take its second chance next weekend.
Young winger Tom Makinson led the way with two tries and four goals, but this was a result built on the quality of Saints' defence.
Their coach, Mike Rush, called it "an outstanding defensive effort. It was a true reflection of the determination in this squad," he said.
Warrington's coach, Tony Smith, said: "We didn't attack as well as we can and we were a bit impatient. We weren't at our best and we needed to be."
Both sides made far too many errors in the opening quarter to build any patterns of play, let alone score any points.
When the breakthrough did come, it was from a different sort of failure of ball security, Louie McCarthy-Scarsbrook passing forward out of the tackle to concede possession.
The Wolves scented their chance. Brett Hodgson chimed into the line, sold a dummy and the home side were ahead.
Warrington's main failing was giving away penalties. Sia Soliola was stopped on the line after three were conceded in quick succession, but the extra work had its effect and the next time the Saints' substitute went for it there was no denying him.
Soliola was also involved in Saints taking the lead before half-time, scooping up a ball lost by Michael Monaghan and sending Tom Makinson away for a try to which the winger added his second goal.
Warrington did their best to turn the second half into a siege, but Ryan Atkins twice passed into touch when he would normally have created tries.
In between, Saints caught them on the counter, Jonny Lomax's burst setting up the supporting Makinson. That was the end of Wolves' hope of reaching the Grand Final by the fast route. They conceded further tries to James Roby and Francis Meli.
Warrington: Hodgson; J.Monaghan, Ratchford, Atkins, Riley; Briers, Myler; Morley, Higham, Hill, Waterhouse, Grix, McCarthy. Subs used: M.Monaghan, Carvell, Wood, Cooper.
St Helens: Wellens; Makinson, Wheeler, Jones, Meli; Hohaia, Lomax; Perry, Roby, Laffranchi, Puletua, Flanagan, Wilkin. Subs used: Soliola, McCarthy-Scarsbrook, Clough, Dixon.
Referee: B Thaler (Wakefield)
Half-time: 6-12 Att: 10,190