Brewster scored his eighth goal in 16 games since joining on loan from Liverpool in January.
"That's where you want him - in the box and scoring goals and if he gets a chance in the box, you fancy him," said Cooper about England Under-21s forward Brewster.
"It wasn't an easy finish - you might look back on it and say he should score but he kept it down well and took the opportunity.
"I was really pleased for him again. I thought he could have got another when he might have gone round the keeper.
"But he was full of running and endeavour again and a goal threat.
"These younger players have to make the most of their opportunities they're being given and that doesn't just apply to him but all of the young players."