The Robins will now face either Hull or Watford at Wembley after goals in extra time from Lee Trundle and Michael McIndoe earnt them a 4-2 aggregate victory.
Fans flooded on to the Ashton Gate pitch at the final whistle as the Wembley dream became a reality but Johnson said: "There´s a way to celebrate. They have got to be happy but they have still got to play this game in 10 days time."
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