The Shrimps arrived at the Crown Ground looking up towards the play-off places but Bentley admits the result on Tuesday night now has them looking over their shoulders at the sides below them.
"I am very disappointed. We were second best in every department and I am not going to make excuses - it was unacceptable," said Bentley.
"Our Achilles heel has been defending from set pieces and we have conceded two goals from corners at Accrington.
"I feel sorry for the fans but no one is hurting more than me - it was embarrassing and we have got to put it right.
"If we had won at Accrington we would have been two points off the play-offs but now we are suddenly worried about getting dragged back into the pack and, if we turn in many more performances like that, we will be.
"We need a centre-half and we need to work on set-pieces - even if it's 10 hours a day! I won't put up with performances like that."
Substitute Padraig Amond replied for Morecambe but Molyneux made it 5-1 with his second goal of the night in injury time.
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