Despite this, Adedire Mebude scored a third for City in the closing stages to ensure we sail through to the fourth round.
With the FA Youth Cup being a significant target for the City academy this season, head coach Ben Wilkinson would've wanted his side to make a strong start as we sought to progress on to the next round.
And his side responded, with O'Reilly coming close to giving us an early lead, hitting the woodwork with just five minutes on the clock.
But it would be second time lucky for the midfielder, as he gave us the lead at Bishop Auckland, striking just after the half-hour mark, and City would hold that lead going into half-time.
Into the second period, City once again were denied by the woodwork, this time with winger Adedire Mebude striking the post.
But just like in the first, we were able to capitalise on our chances, with O'Reilly grabbing his and our second to give us some breathing room against our North-East opponents.
However, City were reduced to ten men as we entered the closing stages, with Luke Mbete sent off following a mass confrontation on the pitch.
But despite the numerical disadvantage, we managed to score a third through Mebude right before the full-time whistle to round off an excellent performance.
HOW WE LINED UP
Ben Wilkinson was able to call up any eligible players from our Elite Development Squad for this game, and his team sheet reflected how he wanted to use those who have experienced Premier League 2 football to boost his ranks.
WHAT IT MEANS
The win over Middlesbrough means City have progressed into the fourth round of the FA Youth Cup.
We will face an away trip to Brighton and Hove Albion, with all ties to be played by Saturday 15 January.
Our U18s are back in league action next week, with a home tie against table-topping Blackburn Rovers in the U18 Premier League North.
Kick-off at the City Football Academy is 12:00 (UK) on Saturday 18 December,
News about Middlesbrough v Man City
City excited by FA Youth Cup opener, says Wilkinson
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