Goals from Luke Murphy, Bradden Inman and Mathias Pogba put the game beyond the hosts' reach before Paul Huntington's consolation.
North End are now winless run at home in the league in six games and Westley said: "We got ourselves to a decent level of form and performance and you know the wheels have come off the wagon.
"The ingredients required to win football matches haven't been shown in the team, and they weren't shown again here.
"We haven't got the team functioning and performing and there's a lot of problem solving to do to recover the ground we've lost in this rocky period."
