THE return of strike pair Martin Paterson and Charlie Austin couldn't inspire the Clarets to victory at Turf Moor.
Instead it was Pompey who were the unlikely winners as skipper David Norris struck deep in to injury time to provide his side's first win on the road in 14 games.
It was a stop-start encounter with neither side packing the impetus to take the initiative. Michael Appleton's resilient unit frustrated throughout, extinguishing Burnley's attempts to push forward.
That growing annoyance forced the Clarets in to various bad habits, with Stephen Henderson more than happy to scoop up overhit passes. Anything that didn't reach the Pompey stopper was wiped up in a domineering aerial performance from the visiting defence.
Pompey almost broke the deadlock early on when Joel Ward's surge forward saw the ball break fortunately for George Thorne who tested Lee Grant low to his right. However, Luke Varney was the first player on the scene but he couldn't force the ball past Kieran Trippier on the post from close range.
The former Blackpool forward went close again when he beat Grant to a 50/50 ball over the top before toppling over in the area after being clipped by the keeper. But referee Steven Rushton penalised Varney for a high foot, which proved his last action of the game as he hobbled off moments later.
Grant spilled a Hayden Mullins strike from 20 yards and Norris had an effort deflected wide for a corner as Portsmouth picked up the momentum. But 0-0 was a fitting half-time result in a game void of energy, desire or goalmouth action. Infact the Clarets couldn't boast a single shot on target at the interval.
The Clarets picked up after the break. Ross Wallace's set-piece flashed wide of the angle, and Henderson tipped a stinging Chris McCann effort over the bar following a flowing move involving Michael Duff, Wallace and Jay Rodriguez.
Substitute Erik Huseklepp went close again for the visitors when Ward found Norris inside the area and the Pompey captain lifted the ball in to the path of his team-mate whose volleyed effort across Grant whistled wide of the far post.
A huge reception followed when long-term absentee Paterson rose from the dug-out to replace the ineffective Junior Stanislas and that change seemingly rejuvenated the home side. Wallace went close with a half-volley, McCann's volley from a Sam Vokes lay-off was deflected wide and David Edgar glanced a header wide from a quickly taken corner.
Further jubilation from the stands arrived in the 74th minute as Austin was introduced, replacing last week's Upton Park hero Vokes but still nothing fell Burnley's way.
Then, in time added on, Pompey broke and the Clarets defence, who had stood firm for 90 minutes, allowed Norris too much time and space on the edge of the box as he guided a low, left-footed effort beyond Grant and in to the corner.
The Clarets didn't contribute enough to the game to earn three points but the late defeat was extremely harsh. The Clarets could have stretched an unbeaten run to four games, instead Pompey registered their first triumph on the road in 14 games.