Moore has only made six appearances for the Black Cats since joining the club in the summer of 2024, but O'Nien says the keeper is an "unsung hero" behind the scenes and was "the most important cog in our machine that won promotion last season".
O'Nien was a regular for the Black Cats last term but has found opportunities hard to come by in the Premier League.
The captain has played in Sunderland's last four games games - starting against Leeds, Port Vale and Newcastle - but got just three minutes of Premier League football in the first half of the season.
That, he admits, was tough, but he used Moore as inspiration on a daily basis.
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"It was really difficult, but opportunities come every single day in training so it depends how you want to frame it," said the defender on BBC Radio Newcastle's Total Sport show, which was held at the Academy of Light this week.
"I had opportunities every single day in training to impact, and contributing to a football club goes well beyond just starting a game.
"If I go down now to my locker here at the training ground, I've got a Simon Moore shirt in there. How many games did he play in our promotion season last year? Maybe around four, with three clean sheets, conceded two goals. So he played four games and he was the most important cog in our machine that won promotion last season.
"I have his shirt in my locker because if I'm not playing, it reminds me to be like him. He is a wonderful human and he puts that first, and then it's the footballer.
"He just has this way of connecting the group, demanding from everyone and just making sure everyone holds the standard of what this club and this city is.
"For me, he'll be the unsung hero of what we've done here. He won't get the mural on the side of a wall but his shirt is there in my locker and I know what anyone who has ever played with him, if they hear this they'll know straight away exactly what I'm talking about. I wouldn't even need to explain it to them."
O'Nien himself is an inspiration to others in the game, having climbed from the non-league to the Premier League.
"I'm very proud, and I've said how much debt I owe to my family and the people who have helped me along the way," he says.
"The funny thing is however I felt playing non-league, I felt the exact same way playing in the Premier League. There's unbelievable pride, yes, but if there's anyone in non-league chasing the Premier League like I was, the thing I'd say is there's no getting here and feeling 'I've made it, I'm done'.
"It's the same feeling, if you don't enjoy non-league you won't enjoy the Premier League. There's no getting to the top of the mountain and thinking, I've done it. The fun work is climbing the mountain because as soon you get there, you're looking at the next challenge."