They had already hinted at their class and vibrancy but a 53-10 sixth-round rout of illustrious opponents in front of the BBC cameras had onlookers gushing.
Desperate Saints, with club legend Keiron Cunningham recently sacked, were at their lowest ebb.
Almost a year to the day, though, when the sides meet once more at Wheldon Road this afternoon, at the very same stage of the competition and with the game being beamed live again, the picture is so different.
This time it is the Merseyside club who arrive full of confidence, verve and panache, standing astride at the top of Super League playing with such swagger.
Australian Justin Holbrook took over the week after their Cup exit last term and slowly started to rebuild; now they head into this contest as overwhelming favourites.
That said, Castleford– still nauseated by their bitter Grand Final defeat to Leeds Rhinos – have not suddenly disappeared.
Granted, they are struggling with key absences given Man of Steel Luke Gale and fellow half-back Benny Roberts are both injured, just like the prolific winger Greg Eden, who scored a hat-trick against Saints 12 months ago.
Powell has also been nervously waiting to see whether full-back Jake Trueman and prop Grant Millington – both concussed in last week’s loss at Hull FC – will be fit to resume this afternoon.
Admittedly, 11 of the 17 that featured in the same game last term could feature again here but it will take some effort to prosper.
Speaking to The Yorkshire Post, Castleford prop Junior Moors conceded: “Saints have been playing some great rugby league and we expect nothing less on Saturday.
“We’re preparing for them to be at their best and we have to be at our best to make it a great game and get over the top of them.
“They have a great pack. All of them are playing really well. They have some great halves and some nippy guys out the back.
“Ben Barba’s in great form, too. He’s a special player.
“He’s in the sort of form that got him player of the year in Australia so we have to be at our best to try and stop what he’ll be trying to do.
“We’ll have to kick high, then get hold of him and make sure he doesn’t get chance to do what he likes to do.”
Australian full-back Barba has certainly been a revelation this term, easily the best player in the competition, and he returns after missing last week’s win over Catalans Dragons to injury.
Recollecting last year’s Cup meeting, Moors admitted: “It was a great day for us.
“Everything was going right for us; we were playing some pretty expansive rugby and it’d be good to replicate that on Saturday again.
“But obviously it’s going to be a tough game this time.
“Justin Holbrook’s been really good for them. He turned their whole season around and that made for a really great game in the (Super League) semi-final here which was a great game.
“We’re obviously expecting a hard match now but the boys are ready.”
Castleford did overcome Saints to reach Old Trafford last September but their rivals then hinted at what might come this year and quickly proved the point with a sobering 46-6 defeat of Powell’s side on the opening night of this campaign. That, though, was an aberration in the big scheme of things for Tigers who, although not proving as fluent as 2017, are still picking up plenty of wins.
Nathan Massey is back from injury to stiffen up the pack and Jy Hitchcox – on loan at Bradford for the last month – could play wing to allow Michael Shenton a return to centre where veteran Kiwi Jake Webster also resumes.
They have not won the Challenge Cup since 1986 and Aucklander Moors admitted: “It’d be great to get to the Wembley final.
“It still burns that loss (Old Trafford) last year and adds fuel to the fire to get to another final in whichever competition. We’ll be going for it on Saturday. It’s a knockout competition so we have to put it all on the line.
“We have some players filling in in different positions and we have to have faith in all the players in where they have to be.
“We’ve trained hard to get those combos right for Saturday and I’m sure we will.”
The former Melbourne Storm front-row, now in his fourth season at Wheldon Road where he is contracted to stay until the end of 2020, is getting back to his best after injury.
He, like all his team-mates, will need to find it today.