Claude Puel felt Southampton were handed an expensive lesson away to Hull City, as they suffered a 2-1 defeat at KCOM Stadium.
Saints took the lead through Charlie Austin's sixth-minute penalty, and looked to be on course for three points against a Hull side that were on an eight-match winless run in the Premier League.
But quickfire goals from Robert Snodgrass and Michael Dawson in the second half turned the game completely on its head and handed the hosts all three points.
Puel felt they Saints had been punished for not taking advantage of the dominance they had displayed in the match.
"Today, we didn't make all the good work, we didn't give all the intensity. We left this team to believe in a comeback, and for us this is not normal. I am the first responsible.
"Congratulations to Hull City, because they believed all the time that they could come back, but I think we can do better to try to score this second goal to keep the control of the game.
"It's not disappointment, but we are angry, because we are responsible. After, of course, we have situations and chances at the end of the game, but we didn't finish the work with the second goal, for example, or keep control of the game and we paid for this very expensively."
Reflecting on only scoring once in the opening period, Puel added: "It was a strange first half, because we had the opponent's injuries, the time stopping, and we lost the rhythm of our game to continue our good pressing, to continue to put this team in difficulty and to score another goal.
"It was a strange first half, it was dangerous, and we saw this. It's a good lesson for the future."