Davis came off the bench to provide the game's late climax
Sean Davis's winner saw Portsmouth edge a thrilling second half over battling Blackburn to earn Tony Adams a first Fratton Park win as boss.
Peter Crouch hit his own post in a lively first period but easily nodded in the opener after 48 minutes.
Jermain Defoe soon slotted in Pompey's second but Blackburn hit back through substitute Matt Derbyshire's looped header and Tugay's fizzing 20-yarder.
Davis clipped in late on to leave Paul Ince's side winless in nine games.
That record means Blackburn are now on their worst league run in a decade and leaves the club sitting 19th in the table.
Former England team-mates Adams and Ince were in opposite dugouts before kick-off and, with both managers still finding their feet in their first season as Premier League bosses, the match was lent an interesting subtext.
Unsurprisingly, showing the confidence of a team that drew 2-2 with Italian giants AC Milan in the Uefa Cup on Thursday, Portsmouth hit the ground running and should have taken a fourth-minute lead.
Interview - Portsmouth boss Tony Adams
Glen Johnson played a sharp pass through to Crouch whose throughball was met by Glen Little, but the Pompey midfielder could only shoot straight at a backpedalling Paul Robinson.
Crouch was proving an influential pivot in attack with the hosts pressing hard and Armand Traore fired a low shot just wide.
But Blackburn did carve out chances as Stephen Warnock miscued from 10 yards out with his weaker right foot before Roque Santa Cruz, after being delicately played in by Benni McCarthy, crashed a low shot just past the post from 18 yards out.
The visitors came within inches of the lead when Crouch, attempting to clear Brett Emerton's viciously inswinging corner, flicked a header on to his own post with David James stranded.
Crouch then should have scored himself shortly before half-time but headed over from six yards after Traore had chipped over a superb cross.
Pompey boss Adams sought to add a touch more composure after the interval as Niko Kranjcar was brought on for Glen Little - and it had an immediate effect.
Marauding Johnson, in outstanding form, swung over a perfect 48th-minute cross, which Crouch steered back beyond Robinson and inside the post for a simple opener.
Minutes later, Croatian midfielder Kranjcar fed Defoe, who turned sharply before bamboozling Christopher Samba and slotting easily past Robinson from 12 yards.
Yet Blackburn showed their steel by getting one back within 10 minutes as Derbyshire, on for Benni McCarthy nodded a deep, bouncing Morten Gamst Pederson cross over David James.
And by the 66th minute they were level as, to their cost, Pompey let Tugay motor forward from 50 yards out before the Turkish midfielder rifled a low shot from 20 yards out just inside James's near post.
Ince 'hurting' after defeat to Blackburn
Blackburn sensed an unlikely victory and Derbyshire again had the ball in the net, only for it to be ruled out for a Samba foul on James in the build-up to the substitute's hooked finish.
Pompey were not finished, though, and midfielder Papa Bouba Diop muscled forward from deep to force a smart Robinson block.
With Blackburn unable to clear their lines from the rebound substitute Davis, on for Traore, pounced on the loose ball before advancing to deftly chip over Robinson from eight yards.
Derbyshire had a late chance to level in a frenetic finish but his reactions were not quick enough to convert Santa Cruz's cross.
Portsmouth boss Tony Adams:
"We've still got some defensive things to work on. We're going through a little phase of surrendering things. This time we knocked off from a throw-in.
"But at least we had the spirit to come back and win it - and on this occasion, a bit more time. I'm delighted with them again. It's a relief to get the win.
"We were not very good in the first half. You can hear from my voice that I had to get into the guys a bit at half-time."
Blackburn manager Paul Ince:
"It was a poor decision from the referee [to disallow our third goal].
"He gave the foul on James but you see on the replay that he hasn't touched him and it should have been 3-2.
"They are the things that happen when you are down there. That is the sort of stuff we have to contend with at this moment in time, but we'll keep marching."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.