"Obviously we got off to the worst possible start," Irvine told Sky Sports. "Jonas has tried to clear it, he's not cleared it properly and it's a fantastic finish by Romelu Lukaku.
"Second half we didn't get out of the blocks as we'd ended the first half. We were probably drawn into the game at that particular time, when unfortunately there was another individual error. We're making some errors at the moment and we're getting punished for them.
"Both players are obviously extremely disappointed, it's not normal for them to do that but it happens and we have to deal with that. Now we make sure we do our work on the training ground and make sure we get a better result next time. I'm sure they will recover from that kind of setback."
West Brom are still winless after four Premier League games this season.