O'Neill said that he believes that Mignolet, 24, will only improve with age and can become a top-class goalkeeper.
"He has been fantastic for us this year," Sky Sports News quotes O'Neill as saying.
"He started on New Year's Day for us when Keiren Westwood was ill and Simon was not particularly fit - in fact he had brought his parents over for the game thinking he was going to be sitting in the stand.
"He played that game with a mask because he had broken his nose and jaw I think, and he has been fantastic since then. With age on his side, he should be a really fine goalkeeper."
The result keeps Sunderland behind Stoke on goal difference, with both teams on nine points.