Ian Holloway admitted he was at the lowest point of his career following Leicester's relegation to League One.
The Foxes slipped out of the top two divisions for the first time in their 124-year history thanks to Saints' 3-2 win against Sheffield United at a packed St Mary's.
"I can't really put into words how I am feeling at the moment," said a disconsolate Holloway whose side went down with the second best defensive record in the second tier.
"This is the lowest point of my career, without a shadow of a doubt.
"I am just bitterly disappointed at the moment because if we had produced performances like that for the rest of the season then we wouldn't be where we are now.
"The spirit, the focus and the work rate was all there but it has been few and far between this season and the table doesn't lie.
"We are in that spot and it is absolutely devastating. You only stay up if you are good enough and the table doesn't lie.
"We didn't get relegated because of this game, it was because of other performances."
Answerable to a chairman who is not afraid to wield the axe when things do not go to his liking - Holloway is ex-Pompey chief Milan Mandaric's fifth permanent manager since he took control of the club in February 2007.
And the City boss admitted he does not know whether he will be given the chance to try and lead Leicester back from League One next season.
"There has been speculation ever since I came here, but that is out of my hands," Holloway added.
"All I do know is I feel I have let my family down and all the Leicester City people. I take full responsibility.
"I thought I could galvanise this lot. I was talking about the play-off and I genuinely believed that, but everything I have touched hasn't really worked.
"Leicester will be back. They are too big a club with too much pride not to bounce back. They deserve better."
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