Sadio Mané’s absence from the starting line-up came after he was late for a team meeting two hours before kick-off, while Victor Wanyama’s red card changed the complexion of an even contest.
Alex Tettey scored shortly after Saints were reduced to ten men, and Koeman felt those two moments with decisive in seeing his side slip to defeat at Carrow Road.
“I am angry. I’m angry about the final result, not about the whole team performance. I think we controlled the game,” Koeman told youtube.com/southamptonfc
“But we punished ourselves because we made individual mistakes. First the situation about Sadio – he came late in the last meeting, two hours before the game.
“That’s unacceptable because we had to change our line-up two hours before the game and that’s not the preparation what we like to have.
“That’s the first mistake of Sadio. The second is the situation about the red card in the game. I think we controlled the game and they scored minutes after the sending off of Victor.
“He has to know, he has enough experience, that you can’t make that tackle and taking a risk when you have a yellow,” continued Koeman.
“That had in my opinion a big influence, both individual mistakes of the players. It’s hard to take.”
Koeman felt his side tried to respond following the goal, but admits Saints find themselves in a tough position at present.
“There was some reaction but after the last results, the mental situation of the players is difficult,” the Saints boss added.
“When it’s going well we can show that belief and confidence, but when we get things against us it’s difficult to continue what we like to do.”