There was 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 sit 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, make his first start in over nine months following a knee injury.
Martinelli impresses again
Martinelli was already a fan favourite 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 was 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.
‘Close to playing for us at highest levels’
Arsenal manager Unai Emery on BT Sport: “To have six points after the two matches, it’s really important. The players, when they did all they can, it is perfect. We did a lot of good, we can analyse to continue to improve. It’s a fantastic victory.
“We can improve in how to keep the ball and make more chances but for the players [on Thursday], they are very tired after playing on Monday and they still played fantastic, it’s a fantastic victory.”
On playing young players: “We have to give the chances to the young players and they take them. They are close to playing for us at the highest levels. They showed that they can perform and they can score. They are playing well, it’s good.”
Arsenal goalscorer Joe Willock on BT Sport: “One of my targets is to get more goals in my game and it’s even better that my goal and my team’s goals has also come with a clean sheet. The manager told us to keep going even if it’s three or four nil. We want to get the ball back and get more goals. He drills that into us.
“We have a manager here who wants to play youngsters and I have to make sure I take my chances and prove why that is the way forward.”
A youthful era – the best of the stats
- Arsenal have won six consecutive home European matches (excluding qualifiers) for the first time in the Emirates era – their longest such run since winning seven in a row between March 2001 and February 2002 at Highbury.
- Standard Liege have lost eight of their nine trips to England in all European competition, with the only exception being a 2-2 draw with Everton during the 2008-09 Uefa Cup.
- Arsenal netted three goals within the opening 22 minutes of a European game for the first time since October 2008 vs Fenerbahce.
- Only Romelu Lukaku (16 years and 218 days) and Mario Gotze (18 years and 105 days) have scored braces in the Europa League at a younger age than Martinelli (since the competition’s rebranding in 2009-10).
- Arsenal’s starting line-up had an average age of 22 years and 350 days; the second youngest in their European history (after Olympiakos away in December 2009 at 21 years and 215 days).
- Manager Emery has won 19 of his last 21 home Europa League matches across spells with Sevilla and the Gunners (W19, D1, L1), including the last six in a row.
Arsenal return to Premier League action on Sunday when they host Bournemouth at Emirates Stadium. Their next Europa League match is at home to Vitoria Guimaraes on Thursday, 24 October.
- Shots on Target