Despite a third successive defeat, Powell was encouraged by the performance of his side, which was transformed from the one that suffered a humiliating 58-16 loss to lowly Hull KR as they overcame the injury woes to lead 20-12 after an hour before falling agonisingly short at the end.
Powell gave a debut to 17-year-old prop Conor Fitzsimmons and was forced to reshuffle his line-up just before kick-off after centre Jake Webster aggravated a hip injury in the warm-up and second rower Junior Moors failed a head test, with prop forward Grant Millington starting the match at stand-off.
"That's just the way it's going for us," Powell said. "I picked three teams today.
"But it was a massive step up. I thought our attitude was great.
"It's tough but if we continue to work that hard, things are going to flip. There is no way with the squad of players we've got that we will continue to lose games.
"If we continue to show the character that we showed today, we are going to start winning.
"We made just too many errors and that really hurt us in that key period in the second half but we weren't too far away today.
"We young kids on the bench but that's no excuse, the boys did us proud, we just weren't quite good enough to win."
St Helens coach Keiron Cunningham was delighted his side managed to back up their close-fought win over Leeds to stay in touch with leaders Warrington.
"The best thing to come out of the game was the way we got out to a lead towards the end and defended it," Cunningham said.
"We were our own worst enemy at times - after every try we seemed to cough up some soft possession to let Cas back into the game.
"The worst thing to happen to us was Cas losing by that score last week. I knew it was going to be a physical encounter regardless of who was or wasn't playing for them.
"It's always tough coming to this place and getting the result whichever way you go about it is the aim and we've done that.
"We can be better but we've gone two in a row and it's something to really build on."
Jonny Lomax, once more switching between full-back and wing on his return from a second knee reconstruction, followed up his two-try performance on his comeback against Leeds with Saints' final try to put the seal on an unconvincing win for Cunningham's men.
"We'd have been happy pinching it by four points but Jonny comes up with a great play, as he always does," Cunningham said. "He was really tired out there but he's a game-breaker."
Second rower Joe Greenwood scored Saints' opening try and he went over in the second half to take his tally for the season to nine.
"That's way I chucked him back out there," Cunningham added. "We needed points and Joe gets points."