Blackburn manager Tony Mowbray singled out Sam Gallagher for criticism after the striker wasted four excellent chances in their 2-1 FA Cup third-round defeat at Birmingham.
Gallagher, who spent the 2017-18 season on loan at St Andrew's, spurned one opportunity in the first half and three after the break.
But Mowbray was unhappy with the striker's finishing, saying: "He works hard in every game. I think at the moment I have faith in him, but he has to score goals.
"He has to get into better positions – we're working hard with him during the week to find better positions to score.
"It was like a tidal wave of crosses coming into the box and he's 6ft 5ins and he should be heading them into the net.
"Yet he's always underneath them, he's always running past the near post, so he has to start listening more as to where he should be going to score, because the ammunition for him was good. He should have been on the scoresheet."
Mowbray insisted his side controlled the game but bemoaned their poor finishing.
"When you control a game like that you have to finish," he said. "It's unbelievable to think we only scored from a penalty, given the amount of play we had around the final third.
"It all means nothing if you don't stick the ball in the net."
Birmingham head coach Pep Clotet praised match-winner Jeremie Bela after his breakaway goal in the 90th minute – with what looked like a cross palmed in by goalkeeper Jayson Leutwiler – sealed an unlikely victory after Dan Crowley's first goal for the club had put the hosts ahead after five minutes.
"Now he is much fitter. When we swapped his side (wing) he showed he is even more dangerous," said the Spaniard.
"Blackburn had a bit of a weakness there. He had the chance and he used it. That's what the good players in the league do."
Clotet was relieved after Blues won for only the second time in 13 games.
"I'm very happy. I like to take the FA Cup seriously – first because it is important for our fans and second because we have been struggling to be solid in the last month," he added.
"The fans have been superb when it comes to backing the players and backing myself through this tough period.
"The fact we can beat a tough team like Blackburn with 10 men with a team dying for the shirt gives me immense pleasure."
Clotet is now hoping this unlikely victory can turn around their recent slump in the Championship.
"When you are not in a good run the most difficult thing is to get a win," he admitted.
"You have this win and the nerves go away a bit. There's confidence coming back."