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Monaco jumped out to a 2-0 lead over Borussia Dortmund on Wednesday in its Champions League quarterfinal match, and it was Kylian Mbappe who opened the scoring the opener in the 19th minute. 

The teenager finished with his thigh, but the goal probably shouldn't have counted. The French phenom was offside by at least a yard, yet it wasn't called by the assistant referee. Take a look:

That's horrendous officiating. What was the assistant referee doing? A big break for the Ligue 1 side, and tough luck for the hosts. 

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