Pompey remain at the summit of the League One table.
The Blues are two points clear at the top of the division after Sunderland were held to a 1-1 draw with Wycombe.
With Kenny Jackett’s side’s game against Charlton postponed, the Black Cats had the opportunity to leapfrog Pompey if they defeated the Chairboys.
Yet Jack Ross’ men failed to capitalise at the Stadium of Light and were forced to settle for a point.
Fred Onyedinma opened the scoring for the Chairboys in the 64th minute.
Josh Maja grabbed an equaliser with six minutes remaining, although Sunderland couldn’t find a winner.
The Black Cats cut Pompey’s advantage at the top of the league to two points.
The Blues sit on 38 points, with Sunderland on 36 after 17 games each.