Pompey’s automatic promotion hopes were left in tatters as they slumped to a shock 3-1 defeat at relegation-threatened York to fall eight points behind the top three.
The Blues began the game looking to bounce back from Saturday’s agonising loss to fellow promotion rivals Plymouth and keep pace in the hunt for third spot.
But hopes of a much-needed win at Bootham Crescent suffered a blow on the half-hour mark when Bradley Fewster rose highest from a corner to head home at the far post after a team-mate had won the first header.
They suffered another dent four minutes later when Lewis Alessandra slotted home from a slick counter-attack from the hosts – tapping in from Fewster’s cross after Enda Stevens had been dispossessed.
And with only three minutes played in the second half it went from bad to worse when Luke Summerfield unleashed a stunning 25-yard effort to give York a third.
Gareth Evans responded for shellshocked Pompey on 55 minutes, although his 10th goal of the season owed much to a goalkeeping clanger from Scott Flinders who let the ball tamely through his legs.
With the Blues throwing caution to the wind, the second half developed into a breathless end-to-end affair with both sides guilty of missing chances.
Michael Smith, Evans and substitute Ben Tollitt all had opportunities to reduce the arrears further, while Fewster and Danny Galbraith were also narrowly off target for the hosts.
In the end, though, sixth-placed Pompey were left to rue a lacklustre first-half display as the gap to the top three grew to eight points with four games to play – albeit with one in hand on those above them.