Pompey’s lead at the top of League One was slashed to two points after their draw at Accrington.
The Blues’ 1-1 stalemate – coupled with Peterborough’s win at Burton – meant they surrendered a four-point at the summit of the table.
Oli Hawkins claimed Kenny Jackett’s side opener on 62 minutes – yet their celebrations were brief as Micharel Ihiekwe equalised just two minutes later.
Craig MacGillivray’s blushes were also saved in the first half when he conceded a penalty, but kept out Billy Kee’s effort.
Pompey dominated the opening 30 minutes but failed to make their pressure count.
Gareth Evans had a 25-yard half-volley stopped by Accy keeper Connor Ripley in the 13th minute, while Ronan Curtis flashed an effort just past the right-hand post five minutes later.
The Irishman had the Blues’ best opportunity of the half on 21 minutes, but he headed Jamal Lowe’s cross against the post.
The hosts started to grow into the game and should have taken the lead when they were awarded a penalty in the 32nd minute.
MacGillivray mishandled Sean McConville’s corner, before he brought down Kee with his legs.
Kee stepped up to take the spot-kick but the Pompey keeper made a superb save to his right to keep out the shot.
Curtis almost broke the deadlock in the 57th minute, but sent another effort against the woodwork.
Pompey did take the lead, though, on 62 minutes.
Evans’ angled free-kick was flicked into the net, with Hawkins claiming he got the decisive touch.
However, John Coleman’s side restored parity just two minutes later.
McConville floated in a free-kick and Ihiekwe’s towering header found MacGillivray’s bottom left-hand corner.
Accrington went close to snatching a late winner but the Pompey keeper adeptly kept out Connor Hall’s swivelling shot.
The Blues held on for a draw, meaning they stay two points clear at the top of the division.
Jackett’s men also extended their unbeaten away streak to eight matches.