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The United defender donned the gloves and became a goalkeeper, even facing a penalty during his cameo in net.
Why did he end up in goal? Well, Edwin van der Sar was replaced at half-time by Tomasz Kuszczak who was sent off in the second-half.
The Pole received his marching orders by referee Martin Atkinson for bringing down Portsmouth striker Milan Baros.
Despite Anderson and Wayne Rooney being inside the box, he was shown a straight red card.
With Sir Alex Ferguson making all of his substitutions, he had to turn to his outfield players on the pitch with Ferdinand burdening the goalkeeping responsibilities.
Centre-back partner Nemanja Vidic and Cristiano Ronaldo chipped in with some words as Ferdinand put on United's keeper shirt and wrapped his hands in a pair of gloves before immediately facing a Sulley Muntari spot kick.
To his credit, Ferdinand dived the right way but he was unable to save Muntari's bullet strike from the spot.
Muntari's goal in the 78th minute settled the clash as Ferdinand conceded just once while between the sticks.
Ferdinand's appearance in goal joins a long list of outfield players ending up in net.
After dumping United out of the cup, 'Pompey' went onto win the competition - beating Cardiff City 1-0 in the final.