O'Neill, without much of his first-choice XI to injury and unavailability, was forced to go in with an inexperienced group - including debutants Will Grigg, James McPake and Daniel Lafferty - and admitted they came up well short as they were beaten 6-0.
"The gulf in class was evident between the two teams," he told Press Association Sport. "We had a mismatch in terms of preparation. We have players who haven't played for five or six weeks since their season finished and Holland have been together for three weeks preparing for a major tournament. It was difficult for us being a bit off the pace against a team who were right on top of their game."
He added: "We took a bit of a spanking, no doubt about that, but we'll lick our wounds and deal with that.
"My selection problems are obvious. We have 10 players out and they're 10 of our more senior players.
"When you come into an arena like this, with 52,000 people, against a team of Holland's class you would like to have as many of your big guns as possible."
There has been some criticism at the decision to schedule a fixture against one of the best sides in the world in a post-season friendly window where Northern Ireland have traditionally struggled with withdrawals.
O'Neill, who was taking charge of the national side for just the second time, stopped short of outright criticism but suggested he the timing of the match had not helped him.
"Losing key players is frustrating for any manager but the main lesson for us is to be a bit more sensible in the scheduling of our fixtures," he added.
Source: PA
Source: PA