Ronald Koeman accepted a portion of the blame for Southampton's 6-1 thrashing in the League Cup quarter-final against Liverpool.
The hosts raced ahead after 39 seconds at St Mary's through Sadio Mane but their evening unravelled after Daniel Sturridge fired a 25th-minute equaliser
England striker Sturridge added a quick-fire second and Divock Origi scored his first Liverpool goal on the stroke of half-time.
One would become three as the Belgium international registered a hat-trick with second-half goals either side of a clinical finish from substitute Jordon Ibe.
Koeman switched to a back three at the interval in an attempt to plot a path back into the contest - a move that he conceded backfired.
"That is not the result we expect," the Dutchman told Sky Sports. "A great start but if you make the mistakes defensively we did in the first half and consider the top quality of Liverpool, then you can lose.
"The second half is my responsibility. I changed the system, I made the risk of three at the back.
"The first goal of Liverpool is a throw in and you see how easily they play, that is not good. The have a great energy and they have qualities in the team.
"We gave them that space, those opportunities and if you give a man like Daniel Sturridge that space he will kill you."
