Pompey tasted defeat for the first time this season after a valiant effort from a second-string side saw them come up just short against Championship Reading.
A minute's silence for the victims of the Shoreham air disaster was followed by a fairly even opening to the game with the visitors heading away a couple of dangerous looking crosses but also forcing Pompey to do some defending of their own as Simon Cox's goalbound effort was deflected wide.
The biggest chance of the half came for Jayden Stockley who could only head the ball over the bar after meeting Kyle Bennett's excellent cross having been fed by a wonderful pass by Danny Hollands.
Reading weren't looking too threatening as Paul Jones was alert to gather any dangerous looking balls and Danny Williams' effort saw him "Quashie" the ball over the Milton End.
It was going to take a moment of quality to break the deadlock and that came from Conor Chaplin as he took the ball around the hesitant Ali Al-Habsi and blasted the ball into the far corner from a tight angle to send over 16,000 Pompey fans into raptures as half-time approached.
Paul Cook's men began the second half brightly too with some attacking moves being nervously dealt with by the Royals defence as Bennett continued to look threatening.
However, all of Pompey's good work was undone in one move as Nick Blackman was given too much space on the left and was allowed to cut inside and slot the ball into the bottom corner to equalise marginally against the run of play just after the hour.
Unfortunately that goal seemed to take the wind out of Pompey's sails and they began to show signs of fatigue with Reading in the ascendency. They couldn't create any clear opportunities against a stubborn Reading back four and were now having to do more defending too.
Steve Clarke's side then took advantage of some slack defending late on to win the game as Gareth McCleary was able to turn the ball home at the far post with neither Jones or any of the Pompey defenders able to cut out the cross.
There wasn't much of a response after falling behind with six minutes remaining. Pompey won a corner in stoppage time and Jones went up for it but the ball was hacked clear and Reading were able to squeak through into the third round of the League Cup knowing that they had been given a run for their money.
Overall, the players can be proud of their performance despite the result. They gave everything and a few of them will be giving Paul Cook a selection headache ahead of Saturday's trip to Luton. Stockley should have scored but he was a tireless workhorse up front, Hollands and Haunstrup were excellent in the first half whilst Chaplin scored another quality goal.
Even if they don't start at Kenilworth Road, they'll have another chance to impress at Exeter in the Paint Trophy next week whilst Pompey fans will be happy to know that if a weakened team can play as well as they did in the League Cup games then that can only bode well for the rest of season in the games that really matter.
Pompey Player Ratings
Paul Jones: 7 - Alert to most of the danger Reading possessed.
Gareth Evans: 6 - Didn't perform too badly in his makeshift role.
Matt Clarke: 6 - Solid enough.
Adam Webster: 7 - Looks like he could play in the first team.
Brandan Haunstrup: 7 - Impressive first half but tired out towards the end.
Ben Close: 7 - Another quality showing.
Danny Hollands: 7 - Looks significantly better than the player we saw last season.
Adam McGurk: 6 - Worked hard.
Conor Chaplin: 8 - Top quality goal even if he faded in the second half.
Kyle Bennett: 7 - Crosses always looked threatening.
Jayden Stockley: 7 - Put the Reading defence under constant pressure despite missing an excellent chance.
Substitutes
Brian Murphy
Christian Burgess
James Dunne (McGurk 79): N/A - Good to see him back.
Nigel Atangana
Ben Tollitt (Chaplin 83): N/A - Got snuffed out whenever he tried to go forward.
Gary Roberts
Matt Tubbs (Bennett 89): N/A - No time to make an impact.