Blues scored three goals during four first half minutes - Alexander Hleb and Nikola Zigic scoring their first goals in Blues colours and Craig Gardner netting his 4th goal of the campaign - earning Blues a 3-1 win against their League One opponents.
"It was a wee surprise in terms of our goalscoring exploits," McLeish said after Tuesday nights game at St Andrews.
"We were clinical in that spell and there was a fair bit of quality on show as well with Beausejour, Hleb's finish and Zigic finally getting on the scoresheet.
"That will do Zigic good tonight, although maybe he could have had a hat-trick.
"We were delighted with Beausejour's contribution, his use of the ball for the second goal. That third goal was great as well from Gardner.
"It gives me food for thought, we've seen some pretty good performances tonight.
"But it was more important we got these guys some minutes towards their full sharpness."