The young Magpies trailed at the break of their opening Group C clash at The Shay following Andrew Oluwabori's opener before Johnny Emerson's emphatic finish levelled the contest towards the hour mark, his maiden strike at under-21 level.
Ben Parkinson's close-range rebound, ultimately, secured maximum points for United's second-string, with Halifax were reduced to ten men in the final minutes following Festus Arthur's dismissal.
The 37-year-old, who arrived at the Newcastle United Academy from Scottish Premiership side St Mirren last week, told newcastleunited.com: "The whole first-half was kind of an anomaly. The player pressed the ball well for their goal, with a little bit of luck, but the lads reacted well.
"I think we were a little too safe in possession first-half, keeping the ball without actually going anywhere and hurting them, but we tweaked a few things, tactically, at half-time and the mindset was much different and better in the second-half.
"It was a great experience for them. That was a real men's game, with a bit of bite, fight and late tackles but that's what you want. In the end, they had to dig in and defend their box, which shows resilience and heart as well. They deserved their win."
O'Carroll's side return to Premier League 2 action on Saturday, 5th October when facing an away clash against Aston Villa Under-21s in the Premier League 2 (kick-off 12pm BST), bidding for back-to-back league wins after a 2-0 win against Blackburn Rovers last week.
Despite his 100 per cent winning start with United's second-string, the Killarney-born coach is confident his side can continue to raise their standards even higher this term.
He added: "I still think we can turn it up another notch and there is more levels to come from the lads but they should be proud of their nights' work.
"I thought we played well in the first-half (against Blackburn) on Friday and then we were poor at times in the second-half. Today, I thought it was the opposite, better without possession but a little bit safe on the ball, in front of people and into feet but that changed in the second-half.
"I'm looking forward to the time when we put it all together and I think we'll be a really good side if we keep improving."
