Though the boss prepared his team as normal, he felt that, for whatever reason, his players weren’t anywhere near their normal standards - and suffered as a result.
“When you have this type of situation you have a big, big problem to point and say we didn’t fight or we didn’t run,” said Pep.
“It is not about that - it’s because we were not prepared to play in this competition, to get to the semi-finals again. We were not ready.
“You have to be prepared for every single game when you play for Manchester City, so today we were not.”
Guardiola also says Kalvin Phillips will need to time to find his best form.
The England star made his first start for City at St Mary’s and his boss says he will find his best form the more minutes he plays.
“(These were his ) first minutes. Step by step. Of course you need time. He was a injured and you need time,” said Pep.
“But it is not about Kalvin, this player or another one.
“When you have nights like today the responsibility is for everyone.
“First the manager of course but everyone as well.”
Watch Pep’s full press conference on the video above.