Chesterfield gained their first league win as Bournemouth crashed to a fifth successive defeat.
Against the run of play, Frenchman Alex Mendy headed the visitors in front, his first goal in English football.
Craig Westcarr cut in from the left to rifle a left-foot shot into the top corner before Leon Clarke completed the scoring from close range.
Tommy Lee made sure of a clean sheet for the visitors when he palmed a Marc Pugh shot on to the bar.
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Bournemouth manager Lee Bradbury told BBC Radio Solent:
"Even though we conceded it's probably the best we've played all season.
"We had the best chances but didn't defend well - you've got to be more ruthless at both ends.
"On another day we could have won this 5-3 but we didn't take our chances and that's been the story of our season so far."
Chesterfield manager John Sheridan told BBC Radio Sheffield:
"When you keep a clean sheet, it always give you an opportunity to win a game.
"We get the second goal and it ends the game. I was very comfortable once the second goal went in.
"Even when you win 3-0, I'm one of those people that looks at things and see what we can do better."