Pompey 0 York 1
Pompey slipped closer to the League Two relegation zone after suffering a home defeat to in-form York.
Michael Coulson scored the only goal of the game in the opening stages with a fine finish from the edge of the box.
The Blues did look an attacking threat throughout, with Jed Wallace particularly effective just behind the front two.
But their hopes of a comeback were hindered when skipper Ben Chorley was sent off early in the second half.
Richie Barker made four changes from the side beaten at Fleetwood the previous week.
Rhys McCabe was handed his debut in a diamond midfield that also included Wallace, while Ryan Taylor and fit-again skipper Chorley also returned.
Ricky Holmes, Wes Fogden, Michael Drennan and Joe Devera were the men to make way, with all four dropping to the bench.
Pompey attacked straight from kick-off and, following a superb bit of skill from Toumani Diagouraga, Wallace’s low cross was just about cut out before it could reach Taylor.
But it was the play-off chasing visitors who broke the deadlock courtesy of a fine finish on four minutes.
Coulson collected the ball from a throw, swivelled sharply and arrowed a fierce shot into the bottom corner that left Trevor Carson with no chance.
It might have got even worse for the Blues moments later, but Carson saved well with his feet after John McCombe had been left in space to collect a corner.
Chorley was then forced to make a perfectly-timed tackle inside the box, as Coulson collected a long pass and bore down on goal.
Wallace was looking dangerous at the other end and embarked on a fine run on 16 minutes. He beat a couple of challenges before sending in a cross that Taylor could only divert into Nick Pope’s arms.
And the teenage midfielder was in the thick of the action again soon after, collecting Taylor’s lay-off and forcing McCombe to make a brave block.
The Blues were looking as fluid as they had for a long time and Wallace scuffed a good chance wide on 28 minutes following some impressive build-up play from Daniel Alfei and Jake Jervis.
Wallace was at the heart of every attack and set up Jervis for a diving header that was saved by Pope, before testing the keeper himself with a low drive from distance.
Pompey continued to push forward as the half neared its conclusion, but they were unable to find a reply before the interval.
Half Time: Pompey 0 York 1
Wallace began the second half as he had ended the first and Pope had to be at his best to turn a powerful shot around the post.
There was also half-chances for both Taylor and Jervis as the Blues looked for a quick equaliser.
But they were dealt a massive blow on 50 minutes when Chorley was penalised for a late challenge on Wes Fletcher and shown a straight red card by referee Roger East.
Jack Whatmough dropped back into the defence to plug the gap, but it was Pompey who were next to launch an attack as Pope kept out Wallace’s effort from 30 yards.
Bondz N’Gala then attempted an audacious over-head effort from McCabe’s corner, with Pope having to pluck the ball from underneath his own crossbar.
Pompey were looking susceptible to counter-attacks, however, as they pushed forward in search of a goal.
One of them led to a free-kick and substitute Ryan Jarvis should have at least found the target from close range after meeting Will Hayhurst’s free-kick on 73 minutes.
Moments earlier Holmes replaced McCabe as Barker decided to throw on some fresh attacking legs.
Carson then did well to palm clear Coulson’s shot as the Minstermen tried to put the result beyond doubt.
And they should have doubled their advantage on 79 minutes as Ryan Bowman somehow managed to miss from six yards out after being teed-up by Ben Davies.
Barker immediately made his last roll of the dice as Patrick Agyemang and Drennan replaced Jervis and Nicky Shorey.
But the Blues were unable to find a leveller in five minutes of stoppage-time and dropped to 22nd in the table.
Pompey (4-diamond-2): Carson; Alfei, N’Gala, Chorley (c), Shorey (Drennan 79); McCabe (Holmes 71), Whatmough, Wallace, Diagouraga; Taylor, Jervis (Agyemang 79)
Sent off: Chorley
Subs not used: Smith, Devera, Bradley, Fogden
York (4-4-2): Pope; Oyebanjo, Lowe, McCombe, Davies; Carson (Fletcher 35 (Jarvis 53)), Penn (c), Reed, Hayhurst; Coulson, Bowman
Goals: Coulson 4
Booked: Penn, Reed, Oyebanjo
Subs not used: Ingham, McGurk, Montrose, Platt, Puri
Referee: Roger East
Attendance: 14,814 (794 away fans)