The hosts led 30-6 at half-time thanks to tries from Daryl Millard, Vincent Duport, Louis Anderson, Steven Menzies and Morgan Escare, all converted by Thomas Bosc, with Josh Thompson crossing for the visitors' sole score.
The Tigers came roaring back after the break, Thompson getting his second, Justin Carney scoring twice and Daryl Clark also going over, but Eloi Pelissier's sixth try for Catalan and a late drop goal and penalty from Bosc made sure the hosts held off the fightback.
Powell had had nearly two weeks to work with his new side, but it started badly for them as Catalan scored in their first passage of possession - Duport sending Millard in to score.
Castleford were level five minutes later after two back-to-back penalties gave the Tigers field position, and Thompson went over to score after being given the nod on the video referee's approval. Jamie Ellis converted to level the scores.
Catalan continued to press and were rewarded after Bosc's 40-20. From the scrum Bosc fed Duport for the French centre to go over to the left of the posts. From the restart, Anderson went over for the Dragons and four minutes before half-time the home side registered two more tries from Menzies and Escare, with Bosc converting both.
With Powell's words ringing in their ears, the Tigers shocked the crowd with two quick-fire tries after the break, with Thompson scoring and Ellis converting.
From the restart, Castleford shifted the ball to the left-hand side and sent Carney clear down the left wing and he raced in from 80 metres out, with Ellis again adding the extras.
Then Anderson took the Dragons to within one metre of the Castleford line and Pelissier picked up the ball, dummied and dived over to score. Bosc converted to take the score to 36-18.
With 15 minutes to go the Tigers again went over twice - Tansey and Grant Millington sending in Clark first of all. From the restart the ball was shifted to the left by Chase to send Carney in for his second try of the night. Ellis converted both to take the scores to 36-30, but Bosc settled matters with a drop goal and then a penalty to complete the scoring.