The Black Cats boss has heaped praise on his Belgian goalkeeper but bemoaned his side's inability to convert chances after a frustrating draw at the Britannia Stadium
The Belgian made a series of crucial saves as the home team looked the likelier side to break the deadlock.
The pick of the bunch was a point-blank block from Robert Huth near the end and a diving save to deny Peter Crouch.
Mignolet suffered a horrific injury last October in a collision with then-Aston Villa striker Emile Heskey when he broke his nose and jaw.
O’Neill said: “He has been fantastic for us this year and going back until he got back into the team second time around.
“Simon started on New Year’s Day for us when Keiren [Westwood] was ill and Simon wasn’t particularly fit. In fact, he brought his parents over for the game thinking he was going to sit in the stands.
“He faced that game with a mask because he was recovering from breaking his nose and jaw.
“But he has been fantastic. With age on his side he should be a really fine goalkeeper.”
O’Neill was content with the point at Stoke, but bemoaned his side’s inability to trouble the opposition.
The Black Cats failed to test Stoke goalkeeper Asmir Begovic and have registered only 12 shots on target in the league all season.
O’Neill added: “A point away from home isn’t too bad. We’ve drawn a lot of those games this season and just not been able to turn some of those draws into victories.”
Stoke boss Tony Pulis believed his side did enough to bag the points.
The 54-year-old said: “If one team was going to win it would have been us.
“Their keeper was outstanding and when we needed a break we didn’t get it.
“We were dangerous from set pieces. There were two in the first half and I don’t know how they stayed out.
“The main thing is that we created a few chances but we need our strikers to score a few goals.”