Gareth Barry struck twice in the 4-0 win, while Gabby Agbonlahor also broke his scoring drought. O'Neill said: "We had hit the buffers. We played so well at Arsenal a month ago and if someone had said then we would collect only one more point from the next four games, I would not have believed it.
"We did not create chances in those games and the confidence starts to ebb away. Today it returned.
"The first goal was important and we looked as if we could score.
"They had a good spell just after half time but overall I was delighted with our performance."
Ashley Young recaptured the form on the left wing which had brought him England recognition after being given a free role by O'Neill.
He added: "We let him go free today and he enjoys that. He can go down either flank and cause problems. He was brilliant today."