Newcastle won their fourth round replay in midweek.
"I was so proud of the whole club against Newcastle because I thought we showed so many people what we are all about," Robinson wrote in his column for the Oxford Mail.
"Did I read somewhere that more people watched it than any Premier League game this season?
"That in itself is amazing and I'd imagine a lot of people were glued to their TV set when we started to get back into the game.
"It was a great free-kick from Liam Kelly and then a superb volley from Nathan Holland.
"Even then, I thought we might somehow manage to nick it inside 90 minutes, such is the crazy nature of the competition.
"If we had won it would have been one of the best comebacks this club has ever seen.
"Instead, our hearts were broken just as I was starting to get the list of penalty-takers straight in my head.
"I was absolutely devastated to see that winning goal go in, because we deserved to at least take the game to penalties.
"Good luck to Steve Bruce and Newcastle – I honestly hope they win it now because they were brilliant with us, but we won't sit and wonder what might have been."