Arsenal's defence was "too soft" to cope with Stoke during their 3-2 defeat at the Britannia Stadium, according to manager Arsene Wenger.
The Gunners conceded three times in the first half - including a goal after just 19 seconds - before mounting a fightback after the break.
"I think we were a bit inexperienced at the back," he said.
"We couldn't play Laurent Koscielny or Nacho Monreal and we were maybe a bit soft to cope with what they offered."
Koscielny, who started the previous two matches, was on the bench but deemed fit not enough to start, while Monreal was injured.
Kieran Gibbs played at left-back, with Calum Chambers partnering Per Mertesacker in the heart of defence and 19-year-old Hector Bellerin making only his second league start.
The quartet found it difficult to cope with Stoke in the first 45 minutes, with Peter Crouch getting the early goal before Bojan and Jon Walters burnished the lead shortly before half-time.
Arsenal last found themselves at least three goals down at half-time in March 2014 away to Chelsea, when they went on to lose 6-0.
And in the previous month, they were 4-0 down against Liverpool after just 20 minutes and went on to lose 5-1.
"There's a lot of regret, we had given a lot," added Wenger, whose side fought back in the second half with goals from Santi Cazorla and Aaron Ramsey.
"We showed great energy levels and a great response. The spirit of the team was fantastic.
"Defensively, we missed the start of the game. We gave easy goals away. We were not decisive in challenges.
"Once we were 3-0 down, we had a mountain to climb. We did climb, but were a bit unlucky I must say."