Morten Gamst Pedersen's early free-kick was cancelled out by a Chris Whelpdale header before the turning point arrived on the stroke of half-time when Posh goalkeeper Joe Lewis was sent off after conceding a penalty, which was duly converted by Steven Reid.
George Boyd managed to equalise for Peterborough five minutes into the second half but Blackburn pulled clear magnificently with further goals from Michel Salgado, Benni McCarthy and Nikola Kalinic.
BreakthroughTalk of swine flu in the Blackburn camp had dominated the build up to the match but the hosts looked anything but sluggish in the opening stages and 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 Jason Brown and in.
Blackburn almost found a response five minutes later as Hoilett connected with Pedersen's cross, but after the ball had bounced to him, Kalinic sent his header narrowly over the bar.
A scrappy period ensued and the visitors looked the more likely to add a second, with Whelpdale unlucky to steer a shot wide from Boyd's cross.
But 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.
Red cardLewis 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.
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 Brown with his left foot.
Blackburn then wasted a glorious opportunity to regain the lead as Hoilett fed a tricky ball across the box, Brett Emerton failed to make contact and then Pedersen blazed his shot over the bar when it seemed easier to hit the back of the net.
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 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.
Blackburn RoversTeam StatisticsPeterborough United5Goals221st Half Goals19Shots on Target37Shots off Target16Blocked Shots812Corners411Fouls113Offsides11Yellow Cards00Red Cards157.9Possession42.1