Vicente’s two-goal blast condemned Pompey to another heartbreaking defeat at Brighton.
The substitute made the difference as the Blues went down to a 2-0 loss on their first visit to the Amex Stadium.
Vicente’s 75th-minute free-kick and stoppage-time second make it a bleak day for Michael Appleton’s men.
It was made all the more frustrating with the free-kick for the game’s decisive moment being disputed.
David Norris was left fuming when ref Mike Dean decided he’d brought down the Spaniard, who then fired a low drive past Jamie Ashdown.
Pompey withstood an early Brighton barrage but settled into the game as it wore on.
Scott Allan could have given the visitors the lead five minutes before the break when he lobbed narrowly over following Peter Brezovan’s poor clearance.
It looked like Pompey would pick up a plucky survival point - but that all changed with Vicente’s entrance changing the game.
The result gives Pompey a mountain to climb with 11 games left of the season.
The Blues are now eight points from Championships safety and rooted to the bottom of the table.