A late strike from new loan recruit Jordan Obita earned Pompey a 2-2 draw at Colchester.
Luke Rodgers put Pompey ahead in the first half with a well-taken finish after Liam Walker’s perfect through ball.
But the hosts hit back on the stroke of half-time, after a fabulous long-range effort from Michael Rose gave Blues keeper Mikkel Andersen no chance.
Both sides had their chances in the second half.
Pompey perhaps just edged it in terms of goal opportunities, though, with Izale McLeod unable to take a couple of clear openings, while Walker struck the outside of a post with a low drive.
Michael Appleton’s side appeared to be heading for a gut-wrenching defeat when Magnus Okuonghae rammed home from close range as he latched on to a corner just seven minutes from time.
Pompey, however, had other ideas and responded superbly moments later.
A marvellous run by Mustapha Dumbuya saw him charge down the right flank to find Rodgers, only for his effort to hit the foot of the post.
But Obita, who had only just come on following his loan move from Reading, was in the right place at the right time to tap home the loose ball and send more than 1,000 travelling fans wild.