Ralph Hasenhüttl identified a number of defensive mistakes as the main contributor to Saturday's defeat at Newcastle United, having conceded three goals in 45 first-half minutes.
Saints were architects of their own downfall at points in the first period, with Jan Bednarek turning inadvertently into his own net - a slice of bad luck - while a mix-up between Alex McCarthy and Ryan Bertrand gifted Miguel Almirón Newcastle's third goal.
Debutant Takumi Minamino was on target for Saints during a dramatic afternoon of football, with Newcastle finishing the tie with nine men, while captain James Ward-Prowse hit another sublime free-kick. Neither of those moments affected the eventual outcome however, with Hasenhüttl concluding that the overall performance was below par.
"If you concede the goals we did today, this is a problem," the manager asserted. "It can't be that every chance is a goal, this is impossible in the Premier League.
"We must find quick the way back to better defending; if we don't do this then it's very tough to win games.
"In the second half, we had a few good moments, but I must say after being two men up it was not good enough. We didn't create enough chances.
"A few chaotic situations in the box but this is not good enough. We need to do it much better. They defended well, and we didn't do it well enough.
"It's clear when you concede so easily the goals, it's always tough to come back. It's really disappointing that we don't take points in the moment. We have to fightback as quickly as possible.
"The pitch was deep and we're trying to create chances, but even so we have to have better counter-pressing. The crosses were horrible, always on the ground and not in the air when we have players like Jannik [Vestergaard] in the box. We had players to be dangerous there. All in all, not good enough."