The Blues finished 3-3 with Stanley in a rollercoaster affair at the Wham Stadium.
After going into half-time 2-0 down, the visitors thought they’d snatched all three points in second-half stoppage-time when John Marquis swept home an acrobatic finish.
The striker had reduced the arrears earlier in the period before Ryan Williams equalised.
However, Marquis would net an unfortunate own goal only moments later to earn Stanley a point.
Yet Pompey are still up to sixth in the table after Charlton also conceded at the death to drop two points against Crewe at The Valley.
The Addicks led twice through Jayden Stockley and Alex Gilbey. However, Owen Dale’s second goal of the game in the 96th minute gave the Blues’ promotion hopes a fillip.
Charlton sit eighth and two points behind Pompey but have a game in hand.
Meanwhile, Blackpool are up to fifth and two points clear of Danny Cowley’s side after defeating fourth-placed Sunderland 1-0 at the Stadium of Light.
Sullay Kaikai notched the only goal of the game for the Seasiders in the 56th minute.
Blackpool also have a game in hand over Pompey.
Meanwhile, Lincoln are up to third and their place the play-off is virtually confirmed.
Jorge Grant’s 11th-minute goal earned Michael Appleton’s men a 1-0 win at Shrewsbury.
As a result, the Imps have moved six points ahead of the Blues with three games remaining but have a greater goal difference of nine.
Peterborough missed out on a chance to seal automatic promotion after drawing 2-2 with Doncaster.
The Posh had raced into a two-goal lead through Joe Ward and Sammie Szmodics inside 23 minutes but Donny hit back with goals from Fejiri Okenabirhie and Taylor Richards.
Peterborough will go up if they draw with Lincoln this weekend.
Pompey travel to AFC Wimbledon on Saturday, who have yet to secure their safety after they drew 3-3 against relegation rivals Rochdale at Plough Lane.
Meanwhile, Burton picked up a 5-2 victory over Fleetwood Town at the Pirelli Stadium.