The Juventus striker bagged in extra time to send Gareth Southgate’s side out and setup a clash with France in the final on Sunday.
Kieran Trippier opened the scoring after just five minutes, curling a free-kick past Daijel Subasic, before Ivan Perisic’s second half goal took it into extra time.
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And Mandzukic described Croatia reaching a first World Cup final in their history as a miracle, and said they would fight just as hard on Sunday.
"This is a miracle. Only great teams can be as brave as we were and fight back from a goal down against teams like England," said Mandzukic.
"We've played our hearts out throughout the tournament. I am happy with my performances so far but I am here for the team. We were like lions out there tonight and we will be the same in the final."
Croatia manager Zlatko Dalic added: "We are deservedly in the final.
"What the lads played tonight is fantasy, they've made history. We haven't said our last word, there is still one more game to go. God willing, we will be world champions."