Guardiola admits his "gameplan was wrong" on the day.
But Walker said: "He's the last man I'm going to question on tactics because he's a genius for what he's done. For the years I've been here, he's transformed me as a player.
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"How he's transformed some of the players in there. If he says that it's down to him. For me it's the whole squad.
"We've got 97 minutes to win a game of football. We all take accountability."