Keown says Johnson's clash with Manchester City fullback Aleksander Kolarov will be key at Wembley.
He wrote in the Daily Mail: "Sunderland need Adam Johnson to be on top of his game. He’ll feel he has something to prove against his old club. For Kolarov, playing against a former team-mate can give you an edge. He has the pace to deal with Johnson, but when the Sunderland player cuts inside, he is tricky to handle."
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