The incident came after five minutes at the Stadium of Light and is likely to remain a major talking point for some time.
Bent's shot from inside the box struck the large red beach ball, which had "Liverpool" emblazoned across it, and the match ball was clearly deflected away from goalkeeper Pepe Reina as well as making things awkward for defender Glen Johnson.
Liverpool's players protested but the goal was allowed to stand.
Pictures on Sky TV showed a young fan in the Liverpool section throwing the beach ball on the pitch and then looking particularly glum at half-time as he perhaps considered the consequences of his actions.
The rules state the referee has the option to allow play to continue if a "second ball" goes on to the field but should call a halt if it interferes with the action.
It also states he should stop the game in the case of "any kind of outside interference" but in reality matches are routinely allowed to continue with items like balloons on the pitch.
Former FIFA referee Graham Poll told the BBC the referee should have stopped the game and given a drop ball.
"If that's the case then we've got away with one," Sunderland boss Steve Bruce told the BBC.
"I didn't know that was the rule to be honest. I hope that doesn't become the main issue as I thought we deserved to win overall, but I'm sure it will."
Bent, whose goal took his tally to six in five games, said: "The beach ball was sitting there in their six-yard box so if they leave it there they pay the penalty."
TOUCHLINE BUST-UP
Bruce and Liverpool boss Rafa Benitez were also involved in a furious touchline bust-up in the second half, with officials stepping in to separate them.
The Spaniard had calmed down when asked about the beach ball incident, saying he did not really see it.
"I was surprised as the linesman was there," said Benitez. "The players explained it to me but you cannot change it."
He was more concerned with another poor performance that has left his side in eighth place, trailing seven points behind leaders Manchester United and six adrift of Chelsea.
"We didn't play well and we didn't have the luck with the goal so altogether it was difficult," said Benitez.
"We had some chances, but not very clear, and they did too on the counter-attack."
Benitez said he had not given up on ending the Anfield title drought that dates back to 1990.
"Chelsea have lost two games, people say that it's impossible if you lose four ..." he said. "I think this year the top sides will lose (more) games and I think there will be more competition."
Fernando Torres and Steven Gerrard missed the defeat and Benitez said they were 50-50 for the midweek Champions League match against Olympique Lyon.
