The League Leaders’ Shield winners did so in breathless fashion last night following a 23-22 golden point extra-time victory at a sold-out Wheldon Road.
But relieved Castleford looked like they had thrown away victory after letting a 20-10 lead slip in the final 11 minutes.
Saints, seeking to sneak into their 10th Grand Final, hit them with a three-try blitz to lead 22-20 and leave the title favourites’ entire season on the brink of ruin.
However, referee James Child awarded a penalty with just 28 seconds to go after Ryan Morgan obstructed Castleford captain Michael Shenton.
Luke Gale – just over two weeks after having appendix surgery – levelled and then stuck the match-winning drop-goal in the 86th minute.
As Castleford bid to win a first league championship in their 91-year history – the winners of tonight’s game between Leeds Rhinos and Hull FC will face them at Old Trafford next Saturday – Powell admitted: “I’ve not really got my breath back.
“It was unbelievable at the end. It looked like we’d thrown away a 10-point lead and when they scored at the end you just need to get the ball back.
“We did that with a great restart and then for Galey to kick those two points was brilliant.
“To go into extra-time, it becomes interesting with the seven-tackle rule; you really have to be careful of what you go with.
“I think we went too early with Luke’s first attempt and gave them those seven tackles as they did to us as well.
“But that drop-goal was world class and to get it over the top of the chasers was pretty special.”
On Gale’s fitness, Powell added: “He looked okay on Monday but I wanted to check on Wednesday he was fine.
“It was a phenomenal effort for Luke to get himself on the field. He’s come through okay – but might have hurt himself when everybody dropped on him! I’m delighted for everybody at the club that we’ve made the final.”
St Helens coach Justin Holbrook, who has turned Saints around after replacing the sacked Keiron Cunningham in May, said: “It is really hard to take. I’m proud of how we kept fighting. It can be a cruel game at times – and it cost us.”