Omari Hutchinson canceled out Marcus Rashford's early opener for United.
“I think we certainly could have won it, so you could look at it that way, it depends on your perspective, I think,” said McKenna afterwards.
“I think we were certainly the better team in the first half overall and I thought as the first half went on we really grew in ascendancy, and went into half-time in real dominance.
“But the second half, Man United had some good periods of control as well and we had to defend on shape and show good discipline, although we still had a couple of big chances to win it.
“We certainly could have won it, but when you concede an early goal against Manchester United with the motivation they were playing with today, the game could also get away from you in another direction.
“So the main positive is it didn’t and we were more than competitive through the game and everyone represented themselves very well.”
Andre Onana made three crucial saves on the night.
“I thought his save from Liam (Delap) was incredible,” McKenna continued. “I’ve been told he saved it, I thought it hit his head, to be honest, but if he’s saved that from that range, it’s an incredible save.
“The save in the second half was probably a big one, I’ve not seen it back but that was maybe the clearest chance in the second half, so that’s a really good save, and he’s a good goalkeeper.
“I think we probably had the better chances in the game, but it was an even game in other parts and a competitive game. We certainly felt like we could have won it, but there were big positives in how we played.”