The first match finished all square at Fratton Park on Friday night.
Pompey took the lead in the 37 minutes with a strike from Marcus Harness before Oxford United equalised during injury time at the end of the first half.
The teams were unable to be separated after 90 minutes and Extra Time.
Pompey fell to defeat in the penalty shoot out losing 5-4.
See all the best photos from the first half action.
17. Oxford vs Portsmouth
Christian Burgess holds off Matty Taylor of Oxford United. Photo: Michael Steele
18. Oxford vs Portsmouth
Cameron McGeehan is challenged by Matty Taylor of Oxford United Photo: Michael Steele
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