Ralph Hasenhüttl lamented the ease with which Arsenal's first two goals were scored, as Southampton let an early lead slip on the way to a 3-1 defeat at St Mary's.
Stuart Armstrong put the hosts in front after only three minutes, slamming home a wonderful strike from a cleverly-worked James Ward-Prowse corner, but Nicolas Pépé quickly equalised before Bukayo Saka struck later in the half.
Alexandre Lacazette rounded things off after the break, but it was the manner in which Saints allowed their lead to slip that most frustrated Hasenhüttl.
"Two goals we gave away too easily, and then it's difficult to fight back against such a side," he said.
"It's always frustrating when you concede goals, but when it is that easy I think it hurts even more.
"The first was a mistake in the build-up, but then still we had the chance to defend it and we didn't do it, and then the second one was similar.
"It's not the way we can defend, we can do it much better and we know this. After being down one at half-time it's difficult to come back. We had chances to do it, but also the final quality was not good enough.
"We know we are a good side when we play a perfect game, but today we were far off this."