Arsenal had struck first in Portugal when William Saliba nodded home a corner before Goncalo Inacio grabbed one back in the exact same fashion.
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Sporting took the lead after the break through Paulinho but Arsenal equalised from a freak goal when Granit Xhaka's pass hit Hidemasa Morita and trickled in.
But Martinelli was denied a truly breath-taking strike when he raced through on goal from his own half, beating three players and the goalkeeper Antonio Adan.
However, Jeremiah St. Juste matched him pace for pace and was on hand to block the Brazilian's strike on goal with an incredible piece of defending in arguably the game's moment of biggest quality.
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Speaking on talkSPORT commentary, Jim Proudfoot and Dean Ashton were salivating at the prospect of Martinelli scoring.
Proudfoot said: "That could have been one of THE best Arsenal goals in Europe."
Ashton replied: "What a run from Martinelli, it deserved a goal, I don't think he knew St Juste was there. But wow! That was brilliant."
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It happened just minutes after Paulinho put Sporting ahead and could have been a glorious equaliser but, as it happened, the Gunners got one anyway.
Just seconds later, Sporting went through on goal once again through Paulinho, who should have doubled his personal tally but blasted over.
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And with the game resembling a tennis match, Arsenal raced up the other end when Xhaka tried to find a teammate with a pass.
But in flukey fashion, the Switzerland international leathered the ball against Morita that took it past a hapless Adan.
While Mikel Arteta would have preferred the win, taking a 2-2 draw back to the Emirates gives Arsenal a slight advantage.
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And with key players like Martin Odegaard, Leandro Trossard and Gabriel Jesus, being able to potentially call on those three could be a huge boost for the north London side.
Ashton added at the end of the match: "I think Mikel Arteta would be pleased just to get out with a draw and with no new injuries.
"And they will really fancy their chances next week with the likes of Odegaard and Trossard back."