January signing Krystian Bielik made his first start in Arsenal colours on Tuesday night, but the teenage prodigy could do nothing to stop Derby County beating the Gunners at the iPro Stadium. Bielik has been told that he will not play for Arsenal's first team this season as Arsene Wenger looks to bed the 17-year-old into the squad slowly, but he has been used by the youth sides, although not as an Under 21 starter until Tuesday. The Poland midfielder put in quiet but tidy performance before Derby's Ivan Calero smashed in a corner to steal the show and all three points in the Barclays Under 21 Premier League. Krystian Bielik breaks away from Alban Bunjaku of Derby County on his Arsenal youth team full debut . Bielik signed for Arsenal for £2million in January but has been told he is not yet ready for the first team . 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. The defeat for Arsenal meant Derby leapfrog them in the U21 Premier League on goal difference, although the Gunners have three games in hand. Derby were on top from the start and went close through Shaquille McDonald, Daniel Crowley and Callum Guy before Jamie Hanson curled two free-kicks against the crossbar. George Dobson aims a pass away from the challenge of Alefe Santos of Derby at the iPro Stadium . Daniel Crowley tries to escape the attentions of Bunjaku, but Arsenal lost and were leapfrogged by Derby . Arsenal looked like holding out but the deadlock was finally broken by Calero 19 minutes from time. Bielik had his effort from a Daniel Crowley corner cleared off the line with a minute to go but the evening was Derby's.
Ivan Calero scored the only goal as Arsenal were beaten by Derby County . January signing Krystian Bielik made his U21 debut for the Gunners . The £2million teenager saw a headed effort cleared off the line late on .