Reading came from behind to inflict Paul Cook’s first defeat as Pompey manager tonight.
The Blues went down to a 2-1 Capital One Cup loss in an entertaining clash at Fratton Park.
But the home fans among a bumper crowd of 18,190 went home pleased with the efforts of their players against the Championship side.
Conor Chaplin’s excellent finish from the tightest of angles raised homes of another scalp for the Blues after defeating Derby County in the last round.
But Nick Blackman’s well-taken solo effort and substitute Garath McCleary’s winner six minutes from the final whistle made the difference.
It proved an even opening with Kyle Bennett looking lively for Pompey.
His eighth-minute cross just evaded Jayden Stockley before Simon Cox’s shot was deflected wide after 22 minutes.
Chaplin then served notice of his danger with a 25-yarder which Ali Al-Habsi smothered.
Pompey were left to wonder how they didn’t take the lead after 27 minutes when Stockley somehow fired wide from three yards after excellent work from Bennett.
Paul Jones immediately did well to keep the scores level moments later, as he smothered Hal Robson-Kanu’s shot.
But it was that homegrown talent Chaplin who did make the breakthrough five minutes before the interval with a moment of clinical finishing.
Al-Habsi and Royals captain Michael Hector got in a mix-up from Danny Hollands’ long ball but it looked as if the chance had passed with the ball not coming down in the Worthing talent’s stride.
Chaplin stayed cool, however, went wide and ripped home a beautiful finish from the tightest of angles.
He then had a chance for his second four minutes after the restart but curled his shot wide.
The second half failed to see as many chances as the first, until Blackman conjured a leveller out of nothing after 65 minutes.
And Stephen Quinn was the orchestrator of the game’s key moment as he burst into the box with six minutes left and cut the ball back for McLeary to puncture Pompey’s hopes of progress.