Pompey's play-off charge was given a boost tonight as Charlton failed to take advantage of their game in hand.
The Addicks - level on 62 points with the Blues - were defeated 1-0 at AFC Wimbledon.
Lyle Taylor netted the only goal of the game for the Dons in first-half stoppage time.
It means both Pompey and Charlton are finely poised with five League One matches remaining - although Lee Boywer's side have a better goal difference.
The Addicks travel to Fratton Park on April 21.