A brace from Lee Tomlin as well as goals from Tommy Rowe, Nathaniel Mendez-Laing and George Boyd sealed an emphatic win for Posh against FA Cup quarter-finalists Millwall, who had equalised through James Henry and had Shane Lowry sent off in the second half.
The Lions have now failed to win in the Championship since New Year's Day but Jackett does not believe there is a link between reaching the last eight of the FA Cup and dropping into the bottom half of the table.
"We had an awful lot of the ball right the way through the game and didn't do enough with it," he said.
"(We had) no cutting edge up front I didn't think and in terms of our defending we didn't have the awareness and Peterborough were capable of breaking from the first minute.
"We've lost five games on the trot now in our division and it seems to have run alongside a very good cup run.
"I don't think the two are connected, I just don't think that we had enough here to be honest."
The defeat leaves Millwall in 14th place , 10 points off the play-off places.