The place erupted three times in a matter of minutes at the end.
First, when Eddie Nketiah turned the ball home in the 90th minute.
Then again after a nervy VAR check confirmed the goal that means they stay five points clear of Manchester City at the top of the Premier League.
Oleksandr Zinchenko, who was excellent in the second-half, summed up the mood as he turned and screamed at the home fans.
Then came the full-time whistle and exactly the celebrations you would expect after a win that could be huge in the context of the title race.
Mikel Arteta and his coaching staff embraced in a group hug, Zinchenko just fell to floor (perhaps partly due to cramp). In the stands, there were limbs went everywhere.
You can hardly blame Arsenal fans. The Gunners have now reached the halfway point of their season, are five points clear and have a game in hand on City.
This was a brilliant, enthralling game and a throwback to the old matches between these two great rivals.
At times it was more like a basketball match and, right up until the death, it was impossible to pick a winner.
Both sides took the lead, but neither had it for long. Marcus Rashford’s opener was cancelled out by Nketiah. Lisandro Martinez then levelled six minutes after Bukayo Saka thought he had scored a second-half winner. In the end, Nketiah took that honour.
Bukayo Saka was oustanding for Arsenal
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Arsenal finished on the front foot, pushing for a winner, and that is how they started too, pressing United high up the pitch.
It was the visitors, though, who took the lead as Rashford capitalised on some sloppy play by Thomas Partey.
First, the midfielder gave the ball away and then Rashford skinned him with a lovely piece of skill before firing past Aaron Ramsdale from outside the box.
It was a goal that summed up Arsenal’s half. They were just a yard off the pace and there was an unusual looseness about their passing.
On one of the few occasions they did click, the Gunners took full advantage to level midway through the first half.
United failed to clear from a corner and Aaron Wan-Bissaka was caught sleeping at the back post as Nketiah snuck in ahead of him to head home.
If Erik ten Hag was frustrated with the defending for that goal, he could have few complaints about Arsenal’s second eight minutes after the break.
Saka stood up Christian Eriksen on the edge of the box, using the yard of space to find the bottom corner with an excellent finish.
Eddie Nketiah scored the winner in the 90th minute
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The momentum of this game felt completely with Arsenal but after a moment of quality they were undone by an individual error.
Ramsdale came to claim a corner but fumbled the ball and Martinez was able to loop a header into the net.
That goal meant the game was, fittingly, impossible to call as it entered the final 30 minutes. The stage was set for someone to be a hero.
Rashford and Saka, the two protagonists of the game, looked the most likely candidates and the latter hit the woodwork after again cutting in from the right.
In the end, it was Nketiah who rose to the occasion as he flicked home Odegaard’s shot from Zinchenko’s cross to score the winner.
An unlikely hero as Arsenal’s unexpected title charge goes on.