Pompey, saddled with debt and being pursued by Her Majesty's Revenue and Customs, will earn more than £600,000 in prize money and broadcasting fees for reaching the FA Cup semi-final but money was hardly on their minds as they celebrated victory against Alex McLeish's men.
Piquionne's goals brightened up a quarter-final tie short on action until he struck in the 67th and 70th minutes, then Liam Ridgewell had an effort ruled out for the visitors despite the ball appearing to cross the line.
Before that, there was little to do for the two England goalkeepers on display, with David James looking to re-establish himself as Fabio Capello's first choice and Joe Hart tipped as a future number one.
They were barely tested during a first 45 minutes short of entertainment and goalmouth action, despite Birmingham having James McFadden in their forward line after overcoming groin problems during the week.
John Utaka, one of three survivors in the starting XI from Pompey's winning team in 2008, took just eight seconds to drill a shot at Hart - but it was not a sign of things to come.
James, Utaka and Hermann Hreidarsson offered a reminder of Wembley two seasons ago when Pompey defeated Cardiff, with the likes of Lassana Diarra, Glen Johnson and Sulley Muntari then sold at a profit but the club still plunging into financial crisis.
Adrift at the foot of the Premier League and with the threat of a nine-point deduction hanging over them for entering administration. the commitment of Avram Grant's men could not be questioned. Jamie O'Hara had been struggling with a back problem but insisted on playing.
In James, Grant has a goalkeeper desperate to get back ahead of Robert Green in the England pecking order and he tidily dealt with Birmingham's only chance of the first half. Lee Bowyer unselfishly set up Cameron Jerome and James denied the striker with a save at the near post.
Aside from Jerome's chance, the tie became a midfield battle with Michael Brown and Bowyer leading each side. One tackle from Brown, on his central-midfield opponent, earned a yellow card.
It meant flowing football did not figure prominently. When Nadir Belhadj did spot the chance of a counter-attack and tried to switch play, his ball to Danny Webber was accidentally blocked by referee Steve Bennett.
Utaka had sight of goal just before the break when O'Hara sent him down the left but he flashed over the crossbar after cutting inside and forcing Stephen Carr to backtrack.
There was more of the same after the restart, with neither side threatening with intent and both defences on top.
The visitors had Roger Johnson in their defence and he was looking for revenge after being in the Cardiff side that lost to Pompey nearly two years ago.
He and Scott Dann at the centre of Birmingham's defence meant it needed something special for the hosts to make an impression - and Piquionne provided it.
The French striker made no mistake from close range for the opener. Steve Finnan put the ball back in the danger area after a corner and found Utaka, Hart looked to have the situation under control but Dann crashed into him and the ball fell for Piquionne to tap in.
Piquionne's second came three minutes later. O'Hara played him through and the striker twisted and turned around Johnson before planting his finish past Hart for his fourth goal in three games.
There was time for James to pull off a stunning double save, although Ridgewell's header from close range looked over the line on replays.