Two tries in a three-minute spell midway through the second half from Australian forward Trent Waterhouse clinched victory for the Wolves, who will meet Leeds at Old Trafford next Saturday in a repeat of last month's Challenge Cup final which they won 35-18.
Warrington, who will become only the sixth club to contest the Grand Final, ran in four second-half tries to thwart Saints' bid for a seventh successive trip to Old Trafford and bring Mike Rush's reign as caretaker coach to a sorry end.
It was no surprise when Saints opened the scoring on 11 minutes. Tommy Makinson had no right to score after taking Chris Flannery's pass with Chris Riley still to beat but he produced an acrobatic dive to get around his man and plant the ball over the line.
It was against the run of play that Warrington took the lead on 17 minutes, with Jon Wilkin conceding possession with a knock-on 30 metres from his own line and Richie Myler combining with Brett Hodgson to get Riley over at the corner.
Hodgson's touchline conversion made it 6-4 but Saints remained unfazed and two tries in a 10-minute spell from Francis Meli and Paul Wellens.
Makinson kicked his first conversion at the third attempt to make it 14-6 but Warrington scored what proved to be a crucial try two minutes before the interval when loose forward Simon Grix charged onto Lee Briers' pass.
The visitors were back in front eight minutes into the second half when right winger Joel Monaghan was first to Briers' high kick and, although he dropped the ball, it went backwards and he had the presence of mind to gather it back up and touch down.
Hodgson maintained his accuracy with his third goal to make it 18-14 and the Wolves produced some tremendous defence to keep their lead intact before hitting a purple patch in which they ran in three tries in seven minutes.
The impressive Waterhouse supported a break by centre Ryan Atkins to score his first before powering through a tiring defence for his second while Riley finished off a smart crossfield passing move to claim the visitors' sixth try. Meli stopped the rot with a consolation try eight minutes from the end.
- Trent Waterhouse