The Reds dominated the early exchanges of the game at Anfield.
But it was Arsenal who took the lead in the 16th minute, with Kai Havertz finishing off a fine team move.
Although Liverpool fought to at least equalise, the Gunners remained resolute and took all three points.
Iraola, speaking to BBC Radio 5 Live, said: “Disappointing for us. We definitely deserved to score but weren’t able. We regret the first 15 minutes until we conceded the goal but I loved after. We changed a little bit by being more brave and aggressive and we put them under pressure. We had some chances that we haven’t finished properly. Also, they have been good defensively.”
