The 19-year-old Bardghji jumped in in the 76th minute and did not have time to be on the pitch for many seconds before he got the home fans to cheer.
With his left foot, he swept the ball past an opponent in a pure magic trick and played forward Fermin Lopez, who could complete his hat-trick.
According to Uefa's live reporting, it was a trick that is patented by Brazilian legend Ronaldinho and is called "Elastica".
Olympiakos reduced to 1–2 on a penalty in the 54th minute and then had an interesting situation.
But just three minutes later, Santiago Hezze received a red card and Barcelona could start the demolition. The team scored four goals after the dismissal.
Marcus Rashford scored two goals and Lamine Yamal made it 3–1 on a penalty.
