The Portuguese centre-half has been impeccable since signing from Benfica last September, becoming a defensive rock in City’s stellar campaign to date.
In fact, Dias has been on the losing side just twice in 41 games this campaign with 24 of those games in all competitions ending with a clean sheet.
“Bringing Dias into the team has changed everything,” said Dunne who skippered City for several seasons.
“The leadership and the confidence that he spreads has changed the outlook - he to me is the big difference.
“In terms of a mentality, we now believe we won’t concede, there's very few individual errors.
“Dias gets people organised and in a defensive shape, certainly for the big games you need someone like that who can control the backline.
“What he’s done this season has been outstanding. We talk about the glory and beautiful football but what he’s given us as a defender has been outstanding.”
Former midfielder Horlock concurred fully with Dunne’s observations during Wednesday evening’s We’re Not Really Here show.
“It’s his desire not to concede, he looks like he loves defending and he takes it personally if we concede,” said Horlock.
“That makes a big, big difference. It’s infectious, that mentality of not to concede. We’ve seen Ederson do it too, and Dias has brought that mindset to the lads, and that breeds to the guys in front of them, too.
It’s a knock-on effect and has had a massive influence on the team.
“He’s massive for us, and, by the looks of it, everyone loves him.
“He's obviously a good character. He’s been an unbelievable signing.”
Both Horlock and Dunne also gave their views on City’s Champions League semi-final opponents on the show.
“It doesn’t get any easier does it?” said Horlock.
“They’re a top team, there’s no doubt and it’s a game where they’ll feel like they have a chance of going through.
“They’re a top team in their own right, but it’s exciting times, fighting on all four fronts, progressing to the semi-final, we’ll take that all day.
Dunne added: “I’m sure playing on the front foot from the start will be the thought, but given how high the stress levels and the nerves were tonight, when the semi-final comes around it doubles again.
“PSG have the experience, they were in the final last year, they’ll be desperate to go one further.
“And they’re similar to us in that they’re a club who expect and want to win the Champions League and they have two of the best players in world football.
“It’s got all the makings of a brilliant match and a really exciting tie.”
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