O'Neil said, "It's probably our worst one of the season, especially in the first half.
"People were misplacing passes and losing duels every time they went long.
"It led to a terrible first half performance that put us in a tricky spot. We gave it a go in the second half with the subs that came on.
"I don't want to make excuses for them regardless of how tired we are. It was a big effort against Arsenal at the weekend but Bournemouth were at Aston Villa the day after.
"There was nothing technical or tactical about it. When they went long (Antoine) Semenyo and (Dominic) Solanke were able to get to it.
"It's one that we have to accept and we have to get back to work to make sure we do better. We want to get players back.
"Hwang (Hee-chan) did well to play 90 minutes tonight but doesn't look like himself yet. (Matheus) Cunha obviously isn't fully fit but gave us something from the bench.
"The injury situation has caused us problems but we added to that with the performance levels."