League One new boys Stevenage collected their first win in the division as Bournemouth finished with 10 men.
Craig Reid swept the visitors ahead as the home defence appealed for offside.
Cherries half-time substitute Harry Arter met Marc Pugh's left-wing cross to equalise with his first touch.
But home skipper Adam Barrett saw red for handling Scott Laird's cross, John Mousinho scored the penalty and Laird crossed for substitute Chris Beardsley to add a third in stoppage time.
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Bournemouth manager Lee Bradbury told BBC Radio Solent:
"We can't take any credit away from Stevenage, they came and played well but it was a frustrating evening from our part.
"I wanted us to get after them a little bit more [after half time] but we weren't quite at it in our closing down.
On the red card: "It has hit Adam Barrett on the arm. I think it was a penalty, but a sending off? We'll have to look at it again.
"I wanted to go for it so I brought big Steve Fletcher on hoping to get a goal."
Stevenage manager Graham Westley told BBC Three Counties Radio:
"I thought it was another satisfying performance to back up what we did at the weekend.
"We came here determined to play on the front foot, determined to win the football match.
"And I thought the lads, after a difficult first-half, grew in stature and even after the blow of the early goal in the second-half the lads showed a good attitude."