Pompey set up a final appearance against Chelsea in May after a 2-0 extra time win against Spurs at Wembley Stadium on Sunday afternoon.
"It's disappointing obviously, a massive disappointment," the Tottenham manager told Sky Sports.
"We had our chances, but couldn't take one.
"We had enough opportunities, but either hit the keeper or missed them and you've got to stick them away when they come.
"Credit to Portsmouth. They kept going and were dangerous on the counter attack. They had pace up front.
"Unfortunately a costly slip by Dawson on a terrible pitch, which is a disgrace for anybody to play on, but that's not an excuse for getting beat.
"Avram Grant did a good job. He set them up well and I wish them every success in the final."