The Gunners were cruising throughout the clash after Bukayo Saka put them 1-0 up against Nurnberg earlier in the contest.
But after several changes were made by Mikel Arteta in the second-half, Karl Hein was deployed in goal, replacing Aaron Ramsdale.
However, the Estonian's pass to Jorginho in midfield ended in disaster as the Italian was pressured by a Nurnberg player.
On his weak foot, the former Chelsea star tried to pass back to his goalkeeper but it ended up flying past him and in the net from 30 yards in comical fashion.
And Arsenal fans were less than pleased, including this one who said: "Jorginho man am I still gonna have to suffer this again this year."
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Another wrote: "Jorginho own goal from the half line, not the most surprising thing I've seen from him."
While a third posted: "The playbook reads the same: press Jorginho."
But at least this Arsenal fan saw the funny side, saying: "Jorginho is washed. That's the funniest OG I've ever seen."
Jorginho had come on in the second-half for Thomas Partey before the goal went in.
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While it is important to stress that this is just a pre-season friendly, this is exactly the kind of mistake Arteta would like to see ironed out at this stage.
As for Hein, the 21-year-old has yet to play a Premier League match for Arsenal and usually is deployed at Under-21 level.
Last season, the goalkeeper made his debut for the Gunners after playing in the League Cup.
Saka had put the Gunners a goal up earlier in the contest after some trademark finishing.
The England international picked up the ball on the right-hand side before cutting in and thrashing one past Nurnberg goalkeeper Christian Mathenia after seven minutes.
Martin Odegaard has given some fears to Arsenal fans, though, after being forced out of the starting line-up before a ball was even kicked.
During the warm-up, the Norwegian was crocked and was replaced with by Fabio Vieira.
It remains to be seen how bad the injury is but Gunners fans will be hoping that the problem is minor.