Mignolet saved from Heitinga and
Sunderland had led early after a superb strike from
Neville said: "I honestly thought it was in and when the ball came back to Jela I thought he was going to score. I thought it was going to be our day.
"It wasn't to be but we are still in the hat.
"It was a great cup tie - it was full-blooded, there were lots of fouls, lots of free-kicks, lots of action, people giving their all. I suppose that is what it is all about."
Black Cats boss
O'Neill said: "I think we started the game brilliantly, got the goal and we were playing very well.
"The equaliser knocked us back, we lost a bit of confidence with it. There was a big surge from the home crowd.
"I thought the second half could have gone either way but they pressed us more towards the end of the game. I am delighted we are still in the hat, I probably would have taken that at the start of the game.
"I thought it was a magnificent double save, really brilliant. I think if we had been beaten there I would have been really disappointed. I wouldn't have been sure we deserved to be beaten.
"I think on reflection a draw was probably a fair result."
Thibaut Courtois's father has denied reports that his son will join Real Madrid once his contract with Chelsea expires in 2016.