Haaland and Mateo Kovacic struck for the 2-0 win.
He later said: "Three points, a perfect start.
"First games are always hard, for everyone, it doesn't matter if you had a pre-season or not. I had a long pre-season but I don't feel perfect, I'm not in the perfect state. It's good to get that win.
"I knew exactly what to do, I think it was a really good goal. I remember last year he made a really good save against me, it had been irritating me for a long time, so yeah, it was a perfect goal.
"The best players are the best on the easiest things. Touching it with your right and passing with your left. That's the important thing. Pep (Guardiola) says this to me all the time.
"I want to get more involved, that's what Pep wants. But in games like this, do I need to be that more involved? That's the million-dollar question. I want to get more assists and become a better player."