The Brazilian, who joined the Gunners from Sao Paulo in his homeland this summer, was given the nod by Mikel Arteta and needed just 17 minutes to make an impact in Switzerland.
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He rounded off a rapid counter-attack as he emphatically finished Eddie Nketiah's deflected cross from the left to put Arsenal in front.
The goal meant so much to the 19-year-old, who cut an emotional figure as he celebrated his debut goal.
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Arsenal took control of the match in Group A, which also has Dutch side PSV Eindhoven and Norwegian outfit Bodo/Glimt.
However, Arteta's men were pegged back just before half time when Mirlind Kryezin scored a penalty for the hosts after Eddie Nketiah fouled Fidan Aliti in the box.
You can also catch the latest updates from the match on our dedicated live blog.
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