It was the Cherries' second defeat on the bounce but their first at home since September.
Marcos Painter's slip allowed Jamie Murphy to slot home the winning goal after 20 minutes.
Howe said: "We lacked that spark. Our big-match players didn't perform and we need them to dig us out of holes sometimes.
"I thought we were the better team and had a lot of possession but full credit to Sheffield united for how they defended.
"They gave us full respect and we huffed and puffed but never hurt them enough.
"We need to win some games, nothing has been decided here, it is a disappointing result but we have to go again. Consecutive defeats hurt everyone badly but we need to bounce back."