Paul Cook admitted Pompey were fortunate at Mansfield as their title dream remained.
Carl Baker’s 56th-minute goal separated the sides at Field Mill, yet an outstanding Blues rearguard display secured it.
Matt Clarke should have been sent off for a foul on the Stags’ Danny Rose, while Rhys Bennett had a goal ruled out for offside.
Yet it was to be Cook’s men who hung on for a 12th away victory of the campaign.
Following Doncaster’s third straight defeat, it means Pompey can still take the title on the final day against Cheltenham.
Plymouth top the table, with third-placed Blues two points behind, as the League Two title race goes right to the wire.
Cook said: ‘Today we were a little bit fortunate to win the game and I am sure we will accept that.
‘For me as manager, we have very good players at this club, I am very proud of them and I’m proud of the club, so to get 12 away wins is an achievement by the players.
‘It’s a shame we haven’t got another away game!
‘We’ve been looking for Doncaster and Plymouth’s results for that long another week won’t make any difference.
‘Great credit to those teams above us – and we are delighted to be in with a chance of the title on the final day.’