Haaland struck twice for City in the 3-1 win.
Iraola told the Daily Echo afterwards: “I think overall we played a decent game, but decent is not enough to take something from this kind of stadium.
“No, you need to have something special. And there have been moments in the game where they've made a difference.
“And when we had, especially with the 2-1, second half, I remember two chances quite clear from Junior Kroupi that I think you trust him in this kind of situations and we don't score.
“And at the end, this is about the moments. If you want to take something against City here, you have to use your moments.
“I think first half they punished us with Haaland. The way we want to play, at the end we accept that there is a risk behind our defensive line and probably the coordination there between the centre backs has not been spot on.
“And against other players, maybe you have time to correct and no one notices. But against Haaland you lose one metre and it's impossible to recover because he's faster than anyone.”
On Haaland, he added: “Sometimes you have to accept he's a difference maker and if you make the smallest of the mistakes, he can punish you like he did today.
“Especially in the first two goals where the timing, the speed, the finishing is top class.”