Anthony Vanden Borre was dismissed on the hour-mark for a second bookable offence following a deliberate handball and the Belgian will now miss nest weekend's FA Cup semi-final with Tottenham.
Blackburn, comfortable in mid-table, should have emerged victorious but for some slack finishing from Chris Samba and some decent goalkeeping by Jamie Ashdown.
A patchwork Pompey team began with some confidence as the fit-again John Utaka burst into space but his finish was straight at Paul Robinson.
Blackburn though battled back as Ashdown's weak punch landed at the feet of Samba but, in the first of two poor first-half attempts for the big Congolese defender, his shot on the turn was kept out by the recovering goalkeeper.
Four minutes later and David Dunn's deep cross had Ashdown back-peddling across his goal only to see Jason Roberts' looping far post header cleared of the line by Ricardo Rocha.
Jamie O'Hara then cleared off the line from Phil Jones' header as Blackburn piled on the pressure.
The hosts were continuing to struggle to play on an increasingly poor surface which was suiting more to Blackburn's direct style and Dunn went close as his 18-year-strike clipped the outside of the post.
Moments before the break, Samba wasted the best opportunity of the half when he found himself a yard ahead of the home defence and from Morten Gamst Pedersen's free-kick placed his header against the post.
As the rain teemed down the football began to wash away as neither side seemed capable of breaking the tedious stalemate in a dreadful second half.
Vanden Borre needlessly earned his marching orders as following a lunge on Martin Olsson in the first half he then collected his second yellow by sticking a limb out to stop a pass getting to the Swede.
With the hosts reduced to ten there was only likely to be one winner but Ashdown was equal to first Olsson's burst and strike and then Roberts' attempt on the turn in a truly substandard Premier League encounter.