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Ronald Koeman has slammed Southampton for lacking "belief, determination, character and mentality" in their limp 2-0 Barclays Premier League loss at Bournemouth.
The Cherries' first home league win over Saints since 1958 sets up Eddie Howe's men to secure their top-flight future, with key battles against Newcastle and Swansea ahead.
Steve Cook and Benik Afobe struck to guide the hosts home, leaving Saints manager Koeman livid with his lacklustre stars.
The Dutchman abandoned his 3-5-2 formation after little more than half an hour, but insisted his players' lack of heart proved far more pivotal in defeat.
"We have played several weeks with that system, but I had to recognise the danger of Bournemouth's left-back (Charlie Daniels) and that was very good from their coach," Koeman said.
"That created a lot of problems, but that's only talking tactics.
"There was also a big difference tonight: how they started the game, how they were hungry and winning challenges that we didn't.
"And that's not tactics: that's belief, determination, character and mentality.
"They were fighting for their lives and we were trying to win the game, and that was the difference.
"All the 10 (outfield players) on the pitch will recognise that they lost more of the battles.
"After the change we made, we had more control in the game.
"We had more ball possession in the second half but we didn't create really big chances.
"It's not good enough. It's always disappointing if the opponent is hungrier than your team."
Koeman confirmed Charlie Austin suffered a hamstring injury and will miss "several weeks", while Shane Long received a kick to the knee and is not expected to be sidelined for long.
Fourth official Kevin Friend passed out and banged his face on the dugout at the Vitality Stadium at the end of the first half.
Referee Mike Dean blew for half-time immediately afterwards, with Friend receiving treatment on the field and later being taken to hospital.
Non-league referee and watching spectator Dean Treleaven stepped in as a makeshift fourth official, with the second half delayed by five minutes.
Bournemouth dominated throughout and fully merited a victory that sends the Cherries eight points clear of the drop zone in their maiden Premier League campaign.
Cherries boss Howe hailed what he hopes can now prove a pivotal victory in his side's bid for top-flight survival.
"It feels like a really big night for the club, beating our local rivals," Howe said. "For our survival hopes it's a massive result as well.
"Our destiny even before the game was in our hands. We certainly have that attitude: we can't rely on other teams to slip up.
"We need to attack things and try to get there ourselves."
Howe confirmed forward Junior Stanislas has suffered a hamstring tear and could be out for six weeks, Harry Arter picked up an Achilles problem and Joshua King an ankle complaint.
"Junior Stanislas has got a tear in his hamstring, so he'll be four to six weeks," Howe said. "That's a real blow to us because he's been excellent.
"Harry Arter has a potential Achilles problem, and Joshua King felt pains in one of his ankles."