Sam Tomkins scored Wigan's third try in their 18-12 win over St Helens
Wigan survived a stunning St Helens fightback to reach their first Challenge Cup final since 2004.
Jamie Foster kicked Saints ahead after a cagey opening but Wigan led at the break through George Carmont's try.
Quickfire tries from Josh Charnley and Sam Tomkins appeared to have wrapped it up for Wigan at 18-2 with 20 minutes left to play.
But, although Foster crossed twice to set up a grandstand finish, Wigan held on to secure a trip to Wembley.
Saints, playing their 11th successive semi-final, were dealt a blow before kick-off when influential scrum-half Kyle Eastmond was ruled out by injury.
Despite that setback, Saints finally broke the deadlock in the 25th minute when Foster slotted over a close-range penalty after Warriors were caught offside.
Wigan deserved it. It's fabulous for the club and it's fabulous that the club are going back to Wembley, which in the 1980s seemed to be their spiritual home. The thing for St Helens is that they have a lot of young boys who have learned some good lessons that will serve them well for the future.
BBC Sport pundit Brian Noble
Wigan hit back with a stunning score six minutes before half-time. It owed much to Charnley, who slipped his marker deep inside his own half and raced upfield before being brought down by Paul Wellens.
But, as Saints desperately tried to re-group, Wigan kept their composure and spun the ball across the field to Carmont, who stepped inside the covering defenders to score, Richards adding the conversion.
Sam Tomkins was denied a try early in the second half when video referee Steve Ganson ruled Ryan Hoffman had obstructed Saints' Jonny Lomax, but Wigan did not have to wait long to extend their lead.
Play was this time spread to Charnley, who raced down the wing before cutting past Francis Meli and Wellens to touch down under the posts and present Richards with the simplest of conversions.
Wigan seemed to have taken a firm grip on the game when Sam Tomkins held off three defenders to force his way over, but Saints hit back as Meli twice sent Foster in at the corner to cap two stunning moves.
Foster landed one of his two conversion attempts to leave Saints needing a converted try to send the tie to extra time.
As the tension grew, with the clock ticking down, Richards missed a last-minute penalty chance to wrap it up, but it did not matter as the Warriors held on to secure their first trip to Wembley since 1998.
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