O'Neil admits they struggled to live with Chelsea on the day, as Noni Madueke hit a hat-trick for the visitors.
He said, "From 15-20 minutes into the game to half time we were the better side. We were in a really good moment. We shoot ourselves in the foot by letting them score from our goal kick and then after half time we come out and give ourselves a tough task.
"From there we weren't able to wrestle back any control and it is difficult emotionally, you end up out of shape and it looks open and easy for Chelsea."
On the start of the season,O'Neil added: "It's been a tough start for us, to play Arsenal and Chelsea. We've got a lot of things to sort out and then when we come up against teams that are more closely matched to ourselves we will cause them a lot of problems."