A masterstroke by coach Kristian Woolf helped turn around a 12-6 half-time deficit and deliver a 26-12 victory as St Helens got their hands on the Betfred Challenge Cup after a 13-year absence.
Castleford Tigers were on course for their first cup triumph since 1986 after an absorbing first 40 minutes played in front of 40,000 fans at a sun-kissed Wembley, the biggest crowd at a rugby league match for 21 months.
But Woolf sent on Grand Final hero Jack Welsby for the second half in place of tryscorer Theo Fages and he helped transform their fortunes as they scored 20 points without reply to deny Daryl Powell a Challenge Cup win in his farewell season in charge of the Tigers.
The consolation for Castleford was the awarding of the Lance Todd Trophy as man of the match to full-back Niall Evalds, who was on the losing Salford Red Devils side in 2020.
It began as Fages, whose gift-wrapped try turned the semi-final Saints’ way, made the most of a slice of luck as Jonny Lomax’s grubber rebounded off an upright, deceiving defender Oliver Holmes, and bounced kindly for the Frenchman to open the scoring.
Lachlan Coote’s conversion made it 6-0 but Castleford turned the game around.
Evalds started and finished a wonderful move from halfway, regathering the ball from Peter Mata’utia’s kick to score an equalising try before stand-off Jake Trueman plucked the ball out of the air following Gareth O’Brien’s high kick for the second.
O’Brien converted both tries for a 12-6 lead as the Yorkshiremen dominated the second quarter.
Fages failed to re-appear for the second half but they soon drew level.
Centre Mark Percival was the first to reach Coote’s high kick and, after the ball bounced precariously close to the touchline, winger Regan Grace worked it back for veteran captain James Roby - who collected a fourth winners’ medal - to touch down.
Video official Chris Kendall agreed with referee Liam Moore’s belief that it was a legitimate try and Coote’s conversion tied the scores.
There was no dispute over St Helens’ next try, scored in the corner by winger Tommy Makinson after Welsby had cleverly changed the point of attack and that restored the champions’ lead.
With the game on a knife-edge, Saints were indebted to a superb tackle to deny his opposite number Evalds and they were forced into more desperate defending after a rare handling error by Roby inside his own half.
But their defence was up to the task and Coote extended the lead to eight points with two penalties before substitute Kyle Amor plunged over for his first try of the season to clinch the win.