Church's smart volley after seven minutes gave Charlton their first away victory this season, exactly 1,000 days since Powell's first win as the Addicks' manager.
In a game of few chances, Church grabbed the only goal when he latched onto a chipped Dale Stephens pass before expertly controlling the ball with his chest and burying it with a cool side-footed volley.
"Simon scored for Wales in what was a big game for them and you could see the confidence in him," Powell said.
"He played well again in the lone role against Belgium and on Thursday and yesterday his finishing in training was superb.
"Goal scorers and strikers want to be out there and I just felt he would add that for us.
"It was a tremendous through ball from Dale Stephens, superb movement from Church in between centre-half and full-back, a great first touch and finished with aplomb.
"I'm really pleased for him."
Powell's side had failed to keep a clean sheet away from home before today and he put his side's first win at the seventh time of asking down to getting back to basics, and felt it was fully deserved.
He said: "We've analysed all the games and felt we needed to get back to basics a little bit because you can't just go out there and think you're going to win any game. You have to earn the right.
"It won't always be easy on the eye even though at times it was today from both teams but you have to change accordingly and we certainly did that towards the end of the game.
"The two-week break has done us good and we've got a little bit of momentum. It was hard-earned today and we had to put up the big red bus for the last 20 minutes and they fully deserved the three points today."
Blackburn boss Gary Bowyer lamented what he described as a "frustrating afternoon" in which he felt Charlton's goal should have been disallowed for handball.
It is the first time Rovers have lost two consecutive games this season and is their second straight Ewood reverse to Charlton, but he felt his side were on the wrong end of a crucial decision.
"We've seen it (the goal) again on the video. I'm not sure which part of the arm it does hit him on but it's quite clear on the video that it's handball, but these things go against you and level themselves out throughout the year," Bowyer said.
"The ball didn't quite bounce for us today and you get done at the other end with a sucker punch which is a handball for their goal and we're disappointed it hasn't been picked up."
Despite that decision, Bowyer was disappointed that his team could not find a way of breaking down the Addicks.
He said: "Credit has to go to Charlton for the amount of bodies they did get behind the ball but it's up to us to be a little bit cuter.
"There was plenty of endeavour and workmanlike performances but we needed more care in the final third."