The Lilywhites trailed 1-0 at half-time to Maxine Colin's goal and Neil was not happy with what he saw from his players in those 45 minutes.
But a chat over the interval tea did wonders, with North End hitting back to score three times through Daniel Johnson, Jordan Hugill and Tom Barkhuizen.
The 3-1 victory was PNE's first win on the road since January 2 and moved them up to fourth place in the Championship.
Neil said: "I was pleased with the second half.
"In the first half when you come away from home you need to be brave, make sure you win your battles, your tackles, your headers - the fundamentals if you like.
"I didn't think we did the fundamentals well enough.
"I'm not so sure Birmingham were much better to be honest, they got the goal but I expected much more from us.
"We didn't do any of the things we until this point, had done well.
"I made the players aware of that at half-time and obviously I got the response I wanted.
"In the second half I couldn't have asked for anything more, they won every second ball, moved the ball well, won the headers.
"When we needed bits of quality to finish moves off, we had that.
"I can't speak highly enough of this squad because so many things have happened over the last few weeks that we've had to contend with.
"We have lost the two captains, we lost Paul Gallagher today who was ill, lost Darnell Fisher who had been ever-present, we've lost Ben Pearson and DJ.
"They are all first-team starters, they are not squad players.
"We have coped with all that, come here to Birmingham and deservedly won the game."
Johnson swept home PNE's equaliser from outside the box, with Hugill then putting them ahead against a club who bid Â£3m for him in the summer.
The third goal was knocked home by Barkhuizen from close range after being teed-up by Sean Maguire.
Expanding on what he told the players in the dressing room at the interval, Neil said: "At half-time I gave them a tough time, I said you could either shrink and go into yourselves or stick your chests out and show everyone what you are capable of doing.
"Winning away from home is not like winning at home.
"At home everyone is on your side, you play with confidence, move the ball about.
"Winning away takes a bit more bottle than that and we had that in spades in the second half."