Shrewsbury needed to win to keep alive their hopes of an unlikely great escape.
But Posh proved too strong going forward and could even afford the luxury of a missed penalty, when top scorer Britt Assombalonga's spot-kick was brilliantly saved by Chris Weale.
Conor Washington netted twice for the rampant visitors while Lloyd Isgrove and substitute Josh McQuoid were also on target as Shrewsbury replied through Jon Taylor and Tom Bradshaw.
Peterborough remain on course for an immediate return to the Championship with Ferguson now looking forward to the play-offs.
He said: "The way we play we've got goals in us. I think a team that can score goals at any time has always got a chance in these one-off games.
"You look at Liverpool. They'll probably win the league because of the amount of goals they've scored.
"We have got that carefree attitude but one-on-one defending we have to be slightly better at as we saw here.
"Whoever we get it will be a tough game. There's three good teams but I think the other teams will know they'll get a tough one off us."
Ferguson was impressed with his side's attacking prowess as they repeatedly caused Shrewsbury problems.
"We made it a lot more uncomfortable than we needed to," he added. "We had a sloppy start, a good start for Shrewsbury, but from that moment we were completely dominant.
"Our football was really good, we were creating chances and the second goal they score is a sloppy one to lose.
"Shrewsbury have had a right go second half, give them credit for that, and there was a great save from the penalty which would have killed the game off.
"We're in a good place at the moment and if we win next week it's six wins out of eight and that's good form."