The Gunners let a one-goal lead of their own slip after Pierre-Emerick Aubameyang had opened the scoring in a classic North London derby, as Harry Kane was also successful from 12 yards after Eric Dier had restored parity.
Spurs could not hold on for a seventh win in a row, however, conceding to goals from Aubameyang, Alexandre Lacazette and Lucas Torreira in the final 35 minutes to slip down to fifth place on goal difference.
A bad day for the Lilywhites got even worse late on when Jan Vertonghen was dismissed for two bookable offences in a match that had a bit of everything.
The hosts were in front inside 10 minutes thanks to Aubameyang's successfully-converted penalty, awarded after Vertonghen - making his first Prem start in more than two months - handled Granit Xhaka's free-kick delivery, picking up the first of his yellows in the process.
That was a just reward for Arsenal following a fast-paced start to the match, but they failed to add to their lead as Aubameyang could not get a touch to Sead Kolasinac's cross and Alex Iwobi shot right at Hugo Lloris from seven yards out.
The match completely turned half an hour in, however, as Dier stooped to glance Christian Eriksen's free kick past Leno at his front post.
Dier ran towards the corner flag and wound up opposition fans and players with his wild celebrations, sparking a melee that also involved members of both sides' coaching staff.
With things beginning to boil over on the field, Rob Holding lunged in on Son and conceded a penalty, which Kane buried to make it eight goals in eight North London derbies - matching the number scored by Emmanuel Adebayor in this fixture during the Premier League era.
The match barely settled down in the remainder of the first half, with Arsenal coming closest to scoring the game's fourth goal through a dipping Kolasinac header that needed pushing over the bar.
After seeing out a spell of Spurs pressure, culminating in Kane's well-taken free kick that Leno was equal to, Ramsey made a positive run in behind and flicked the ball into the path of Aubameyang, who belted a first-time finish past Lloris from outside the box.
Looking nervous all of a sudden, Tottenham were thankful that Dele Alli had positioned himself on the line to block Shkodran Mustafi's shot, which Torreira followed up with a near-miss from the rebound.
Tottenham, winners on just one of their last 25 top-flight trips to this ground ahead of this game, also had chances of their own as Son blasted at Leno following an error from Hector Bellerin.
Bragging rights and a place in the top four would be Arsenal's, though, as Lacazette found the bottom corner with his 20-yard shot via a Dier deflection, before Torreira kept his cool to tuck past Lloris from an angle less than two minutes later.
Then came the red card for Vertonghen, shown his second yellow for a strong challenge on Lacazette, as Arsenal saw things through pretty comfortably to extend their unbeaten run to 19 matches in all competitions.
ARSENAL (3-4-2-1): Leno; Mustafi (Guendouzi 71'), Sokratis, Holding; Kolasinac, Xhaka, Torreira, Bellerin; Iwobi (Lacazette 46'), Mkhitaryan (Ramsey 46'); Aubameyang
TOTTENHAM HOTSPUR (4-2-3-1): Lloris; Aurier, Vertonghen, Foyth, Davies (Rose 82'); Dier, Sissoko; Eriksen, Dele (Winks 79'), Son (Lucas 79'); Kane