Dean Huijsen headed home a first-half corner kick before Justin Kluivert, from the penalty spot, and Antoine Semenyo put the game out of reach with two goals within two minutes early in the second half for the Cherries' second consecutive 3-0 win at Old Trafford.
After their 12th-place finish last season, Cherries are three points from the top four in their third successive season back in the top flight.
"Everything is very close," Iraola said. "We were playing United, if they beat us they would be have been above us. You know, it's a matter of now, in this next week, we could be behind them.
"This win will not disappear, but is not enough for anything. We have to add a lot of points. So, we go again week by week, game by game. I don't think now so early it makes sense to look much to the standings.