Martinelli finished off a blistering counterattack in the 12th minute of Sunday's Premier League match at Old Trafford.
But referee Paul Tierney ruled the goal out after VAR instructed him to consult the pitchside monitor.
The goal was chalked off after Tierney judged Martin Odegaard to have fouled Christian Eriksen in the build-up.
The decision has proved controversial, with some Arsenal supporters believing it should have been awarded.
"If it takes that long how is it 'clear and obvious'," wrote one fan on Twitter.
Another added: "That was never a foul, this ref is against us."
However, others believe Tierney was right to disallow the goal.
DRAMA AT OLD TRAFFORD! 🚨— Sky Sports Premier League (@SkySportsPL) September 4, 2022
Gabriel Martinelli's breakaway goal ruled out by VAR for a foul in the buildup! ❌ pic.twitter.com/1nZBkTfZOc
"To be fair it's a foul," wrote one Arsenal supporter.
United's new signing Antony was making his debut for the Red Devils, following his £85m move from Ajax.
He was involved in a promising moment early in the game - back-heeling the ball to Diogo Dalot, who found Eriksen with a cross at the back post.
But the Denmark international could only volley his shot narrowly wide.
if it takes that long how is it “clear and obvious” 💀— gunnerscentre® (@GunnersCentre) September 4, 2022
it’s a weak call— FCB Carter (@PunkkCarter) September 4, 2022
William Saliba then missed a good chance for Arsenal, firing over the bar from eight yards out, before Aaron Ramsdale saved well Jadon Sancho as both sides pushed for the opening goal.
After Martinelli saw his goal ruled out, he went close again but his near post shot was blocked with his feet by United goalkeeper David De Gea.
The Brazilian went close again minutes later with a header but De Gea denied him for a second time.
🌟 𝐀 𝐍 𝐓 𝐎 𝐍 𝐘 🌟— Sky Sports Premier League (@SkySportsPL) September 4, 2022
It's a dream debut goal for Man Utd's new star signing! 🇧🇷 pic.twitter.com/xxYfaqnLAU
Arsenal were made to pay in the 35th minute of the match when Antony scored a dream goal on his United debut.
After latching on to a through ball from Marcus Rashford, Antony kept his composure to curl the ball past Arsenal goalkeeper Aaron Ramsdale to give the home side a half-time lead.
Speaking at half-time, Sky Sports pundit Jimmy Floyd Hasselbaink said he believed Martinelli's goal should have stood.
🗣 "He's being weak, it's not a foul." ❌— Football Daily (@footballdaily) September 4, 2022
Jimmy Floyd Hasselbaink and Roy Keane debate whether Eriksen was fouled in the build up to Arsenal's disallowed goal pic.twitter.com/EJctcR66xa
"You don't have to touch the ball," said Hasselbaink, referring to the foul given against Odegaard.
"He's not kicked the player, he's just come in contact with him. That is allowed. That is what they want – they want football to be more flowing.
"Why is that a free-kick?"
Featured Image Credit: Sky Sports
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