Peterborough initially made life difficult for their hosts as Chris Whelpdale equalised Martin Gamst Pedersen's early opener, but goalkeeper Joe Lewis was sent off just before half-time for clattering Pedersen and Steven Reid slotted home the spot-kick.
Peterborough managed a second equaliser through George Boyd just after half-time, but Rovers soon made the difference in numbers tell with Michel Salgado, Benni McCarthy and a Nicola Kalinic penalty completing a comprehensive 5-2 victory.
Blackburn went ahead after only three minutes. David Hoilett was brought down just outside the box and Pedersen calmly stepped up to rifle the free-kick over Lewis and into the roof of the net.
Peterborough were not disheartened though, and after Boyd had issued a warning with a dangerous free-kick that needed only a glancing header to finish, the visitors drew level with 17 minutes on the clock, Tommy Rowe crossing for Whelpdale to head back across the stranded Brown and in.
Peterborough shot themselves in the foot three minutes before the break when Lewis brought down Pedersen in the area as the Norwegian midfielder raced onto a poor defensive header. Lewis was shown a red card and Reid put the resulting penalty past substitute keeper James McKeown to restore Rovers' lead going into the break.
It seemed a straightforward task for Blackburn from there, yet within five minutes of the restart Peterborough had levelled again and Whelpdale was involved once more, surging forward and squaring the ball to Boyd, who had the time and space to lash a ferocious strike past Jason Brown with his left foot.
The Premier League side soon made amends though as Salgado struck his first goal for the club, the Spaniard getting on the end of a delightfully lofted pass from Brett Emerton in the 57th minute and slipping it in at the near post.
The man advantage was starting to tell and Blackburn scored their fourth with just under 20 minutes remaining when Kalinic capitalised on an error to play in McCarthy for an easy finish.
Kalinic then added a fifth two minutes later, converting confidently from the spot after Martin Olsson's cross was handled.