EX-BAGGIE Kanu broke Albion hearts as he ended his former club's FA Cup adventure with a 54th-minute winner as Portsmouth shaded this tight Wembley encounter.
A record all-time semi-final crowd of 83,584 witnessed the Baggies dominate a cagey first-half, with Premier League high-fliers Pompey prepared to sit back and bide their time.
Both sides came back out after the break with renewed vigour but it was Harry Redknapp's men who stole the advantage thanks to Kanu's tap-in.
TV replays showed Milan Baros handled the ball directly before the goal but referee Howard Webb waved the Baggies' protests away.
As Albion fans have become accustomed to, Tony Mowbray's men refused to throw in the towel in a pulsating second period.
But a sure sign it was not the Black Country club's day came in the 75th minute when Robert Koren's 18-yard rocket struck the crossbar.
Albion may have been denied their first FA Cup final appearance for 40 years, but they left Wembley with their heads held high.
Thirty-nine goal partnership Kevin Phillips and Roman Bednar were restored in attack as Ishmael Miller and Pele dropped to the bench.
Redknapp made four changes to his Pompey side with Lassana Diarra, Papa Bouba Diop, Sulley Muntari and Kanu coming in for Sean Davis, Pedro Mendes, John Utaka and cup-tied Jermain Defoe.
The first shot of the game came from the Baggies when Phillips made room on the edge of the area and fired just over the bar.
Two minutes later, some neat play by Mowbray's men saw Zoltan Gera's 18-yard strike spilt by David James but Sol Campbell managed to clear before Bednar could get a touch.
Pompey threatened for the first time in the eighth minute when Niko Kranjcar's ball over the top almost set Baros in on goal, but Dean Kiely collected in the nick of time.
Albion were soon back on the attack when Gera burst past a couple of tackles and squeezed the ball through to Phillips, whose low effort from just outside the box was charged down by Glen Johnson.
In the 23rd minute, Baros raced away down the right and drove past Neil Clement, but Martin Albrechtsen managed to get in a crucial block and when the ball was returned back in by Hermann Hreidarsson, Kiely easily gathered Bouba Diop's 15-yard header.
Muntari then tried a speculative effort on goal from a 30-yard free-kick which flew straight at Kiely.
Baros was booked five minutes later after handling the ball deliberately as he tried to break free of Albrechtsen.
Back came Albion and, two minutes later, James spilt a routine header back from Johnson but the England No.1 just managed to gather the ball before Phillips could stab towards the empty goal.
In the 41st minute, Bouba Diop out-jumped Paul Robinson to head the ball to Kanu and the Nigerian dinked it into the penalty area for Baros, who could not stretch far enough to control, allowing Kiely to gather.
Muntari flashed in a 25-yard effort from the left in the final minute of the half but the Baggies goal wasn't threatened as the tie reached half-time goalless.
Pompey were much more purposeful after the break and snatched a controversial lead in the 54th minute.
Baros controlled Johnson's ball into the box with his arm - which was missed by the officials - before holding off Albrechtsen and firing in a volley.
Kiely denied the ex-Liverpool striker with a smart one-handed save low to his right.
Gera then nudged the loose ball away from Hreidarsson but it slid straight to Kanu who prodded home.
Four minutes later, Muntari got to the left-hand byline and cut the ball back for Kranjcar, who horribly mishit his 12-yard shot wide.
Mowbray made a double substitution in the 61st minute as Bednar and Morrison made way for Miller and Chris Brunt respectively.
Pompey were now in the ascendancy and Kranjcar slipped in Baros in the 66th minute with a slide-rule pass which dissected Carl Hoefkens and Albrechtsen.
Kiely slipped as he came out to meet the Portsmouth striker but recovered to pull off a crucial save.
Gera wrestled the ball from Diarra and Muntari on the edge of the area in the 70th minute but saw his strike curl just over the angle of post and bar.
Brunt looked to have played Phillips in behind the Pompey defence in the 73rd minute but the ball just skipped away from the Baggies' top scorer and into the arms of James.
The momentum was back with Albion and Hoefkens did well to keep the ball in on the right-hand touchline and burst inside the box before pulling it back for Koren, whose 18-yard shot beat James all ends up but hit the bar.
Two minutes later, Muntari skipped in between Albrechtsen and sub Do-heon Kim but screwed his shot well wide from 15 yards.
The action immediately swung to the other end and Miller got in behind the Portsmouth defence.
However, instead of pulling the ball back for Kim or Koren, he chose to try and find Phillips and James snuffed out the danger.
In the 84th minute, Kim gave the ball away to Kranjcar who threaded it through to sub David Nugent.
The ex-Preston ace raced to the edge of the box before forcing a fine block from Kiely. Albrechtsen was fouled as he tried to clear.
Albion countered quickly and created their final chance.
The energetic Hoefkens' low right-wing cross was side-footed just wide of the right-hand post by Miller.
Albion piled forward in the dying seconds but could not force extra-time.
ALBION (4-4-2): Kiely; Hoefkens, Albrechtsen, Clement, Robinson; Gera (Kim 75), Koren, Greening, Morrison (Brunt 61); Phillips, Bednar (Miller 61). Subs not used: Danek (gk), Pele.
PORTSMOUTH (4-4-2): James; Johnson, Distin, Campbell, Hreidarsson; Bouba Diop, Diarra, Muntari, Kranjcar; Kanu (Davis 81), Baros (Nugent 72). Subs not used: Ashdown (gk), Lauren, Mendes.
GOALS: PORTSMOUTH - Kanu (54).
BOOKINGS: PORTSMOUTH - Baros (deliberate handball 35).
REFEREE: H Webb (S Yorkshire).
ATTENDANCE: 83,584.
ALBION STARMAN: Carl Hoefkens.
