Krystian Bielik made his full debut for Arsenal U21s yesterday.
The Polish midfielder joined the Gunners in January from Henning Berg's Legia Warsaw.
Bielik, signed from Legia Warsaw in January for £2million, even saw a header cleared off the line in the closing stages of the game but a dream youth team debut wasn't to be.
Derby ranout winners 1-0 thanks to Ivan Calero's strike.