There were less than three minutes between the 18-year-old Brazilian’s first and second goals while team-mate Joe Willock, 20, made it 3-0 before half-time.

Martinelli, who joined for £6m this summer, later set up Dani Ceballos for his first Arsenal goal.

Arsenal sits top of Group F with two wins from two games.

There were 10 changes to the Arsenal team who drew with Manchester United in the Premier League on Monday but no place in the squad for German midfielder Mesut Ozil.

Instead, manager Unai Emery put faith in the likes of academy graduate Willock, Martinelli, and 19-year-old Reiss Nelson – as well as summer signing Kieran Tierney, making just his second start for the club.

All four impressed as Tierney set up Martinelli’s first with a whipping cross from the left before teeing up Nelson’s shot in the build-up to Willock’s goal.

Nelson recorded an assist – feeding Martinelli for his second – before slipping in the Brazilian to tee up Ceballos’ goal in the second half.

It could easily have been more for the Gunners on a very positive night which also saw full-back Hector Bellerin, captain for the night, making his first start in over nine months following a knee injury.

Martinelli impresses again

Martinelli was already a fan favorite after he became the youngest player since Alex Oxlade-Chamberlain in 2011 to score on his first start for Arsenal, against Nottingham Forest in the Carabao Cup.

Two goals in that 5-0 win were the perfect way for the summer signing to announce himself and every time he got on the ball at the Emirates on Thursday the crowd grew excited.

The teenager spent last season playing in the fourth tier of the Brazilian Football League with Ituano but his quality was evident against Standard Liege and he has now bagged four goals after just two starts for the club.

His first of the night was exceptional – a perfectly-timed header at the near post which flew past goalkeeper Vanja Milinkovic-Savic – while his second was equally impressive, cutting on to his right foot and drilling the ball into the far corner.

Both goals drew a smile from Pierre-Emerick Aubameyang on the Arsenal bench, and if the Gabonese striker had not scored seven goals in as many Premier League appearances this season, there may be a case for Martinelli to start more often.

The young Brazilian capped off an impressive night with an excellent assist – showing pace to reach Nelson’s pass before coolly lifting it over the goalkeeper and on a plate for Ceballos to tap in.