Pompey's automatic promotion hopes are no longer in their own hands after they were held to a battling 1-1 draw at Sunderland.
Needing to match Barnsley's result at home to Blackpool - a match the Tykes won 2-1 - they were unable to claim the victory they needed and remain third in the table.
Despite having a game in hand on the Oakwell outfit, they now sit four points adrift of Daniel Stendel's side with two fixtures remaining.
Hopes remain, however, particularly after Luton’s 2-1 defeat at Burton – and the Blues will take huge comfort from their display at the stadium of Light.
In an end-to-end clash, Pompey matched their hosts, who also required a win to keep their automatic promotion ambitions alive.
Tom Flanagan headed the home side in front on nine minutes, before Jamal Lowe netted on 24 minutes to draw Kenny Jackett's side level.
Both teams tried their hardest to claim the three points on offer, but neither could find a second killer touch in front of goal as the game ended 1-1.
In a pulsating first half, the Black Cats were purring during the opening 10 minutes.
Lewis Morgan's overhead-kick, which was spectacularly saved by Craig MacGillivray before smacking off the post, emphasized their early dominance.
And when Flanagan headed home from Max Power's free-kick on nine minutes there was no denying that the hosts deserved their lead.
However, if they thought they were going to have it all their own way, they were sadly mistaken.
As the Blues have proven in this race for promotion, they are no pushovers, and when Ben Close's effort from 25 yards was deflected for a corner it demonstrated Sunderland had a fight on their hands.
That fact was backed up by a goal for the visitors 60 seconds later, when Lowe netted his 17th goal of the season.
Brett Pitman did well to keep Ronan Curtis' cross in play, before delivering the ball to the back post.
Lee Brown saw his header smack against the woodwork, but Lowe was perfectly placed to draw Pompey level from the rebound.
The Blues could then have found themselves easily in front as they began to assert their authority.
Close blocked Flanagan's clearance and raced towards goal as the ball fell kindly to him.
However, his lob over the onrushing Jon McLoughlin was off target, with Curtis also unable to apply the finishing touch at the back post.
The Irishman did find the back of the net just after the half-hour mark, only for his effort to be ruled out for an earlier foul on McLoughlin.
Then came as series of moves at either end that had all packed into the Stadium of Light on the edges of their seats.
Lee Cattermole volleyed over for the Black Cats on 38 minutes, before Nathan Thompson was on hand to deny McGeady after a long ball forward.
Not for the first time in the game, MacGillivray had to be at his best to deny Charlie Wyke in first-half injury time - preventing the front man from netting from close range following a cross from Luke O'Nien.
Then, just before referee Craig Pawson blew time on the half, the Blues went up the other end, where Lowe saw his goal-bound effort blocked by some desperate home defending.
The second half began just like the first, with MacGillivray denying Lewis.
The hosts, once again, had their bit between their teeth and two timely tackles from Matt Clarke and Thompson proved vital as the match continued at a high tempo.
By this stage, Oli Hawkins had replaced James Vaughan up front, while Gareth Evans' introduction followed suit minutes later, replacing Curtis, as the Blues attempted to freshen it up.
Yet the double substitution was having little impact as the Black Cats attempted to up the tempo.
MacGillivray was once again on hand to brilliantly deny Power on 78 minutes, while Thompson was again in the right place at the right time to deny McGeady when the ball was played through to him on the edge of the box.
Substitute Will Grigg was then next to be thwarted by the brilliant MacGillivray, as he diverted his close-range effort against the post and to safety.
Plenty of bluster from either side in the remaining minutes made for a tense finale, but neither could find the winner as the game ended in a stalemate.
It made for a frustrating afternoon, in particular, for hosts, with several players getting themselves involved in a confrontation with the visitors at the final whistle.