Hector Bellerin's stoppage-time goal rescued a 2-2 draw for Arsenal in a pulsating and controversial Premier League clash with Chelsea.
It looked like Chelsea had come from behind to triumph when Marcos Alonso struck six minutes from time, after Jack Wilshere's first league goal since May 2015 had been cancelled out by an Eden Hazard penalty.
But the Gunners would not be beaten and Bellerin punished Alonso's poor clearing header with a fine finish for a share of the points - though there was still time for Chelsea's Davide Zappacosta to hit the crossbar.
Alvaro Morata had missed a glorious chance to give Chelsea a 14th-minute lead and the visitors were then indebted to a Thibaut Courtois save which pushed Alexis Sanchez's shot on to both posts.
Wilshere broke the deadlock, but there were doubts over whether the midfielder should have been on the pitch.
Already booked, Wilshere went down looking for a free-kick on the edge of the area and might have received a second yellow card from referee Anthony Taylor for simulation.
The Gunners' lead lasted just four minutes as Hector Bellerin was adjudged to have fouled Hazard, who equalised with the resulting penalty.
Alonso's effort appeared decisive, only for Bellerin to strike.
Hostilities between the teams will be renewed in a week's time, in the Carabao Cup semi-final first leg at Stamford Bridge.
On an evening when Arsenal's former arch-antagonist found the target, some in Chelsea blue were ruing his absence.
Ex-Chelsea striker Diego Costa scored in his first game since the FA Cup final loss to Arsenal in May as Atletico Madrid won at Lleida in Spain's Copa del Rey, while Morata missed a golden opportunity here.
Shkodran Mustafi and, chiefly, Calum Chambers allowed Morata to ghost on to a hopeful hoof from Victor Moses but with time and space to set himself, the striker passed the ball wide of the post.
It was an open contest. Arsenal pushed forwards and Ainsley Maitland-Niles tripped over his own feet in the penalty area, with Moses in close attendance.
Moments later Sanchez found room to strike a low, right-footed shot.
Courtois touched the ball on to a post and it rolled on to the other upright before the Chelsea goalkeeper claimed it.
Alexandre Lacazette was able to turn Gary Cahill in the Chelsea box and force a smart save from Courtois, before Cech tipped over Tiemoue Bakayoko's effort from a Cesc Fabregas through-ball.
Wilshere was booked for clattering former Gunners captain Fabregas, who claimed his revenge by nicking the ball as his rival shaped to shoot. The Blues midfielder was cautioned before half-time for a challenge on Wilshere.
Fabregas should have given Chelsea a half-time lead but blazed over from a Hazard backheel.
Cech saved with his feet from Hazard before Courtois denied Lacazette again.
Wilshere went down looking for a free-kick on the edge of the area following Andreas Christensen's well-timed challenge.
Fabregas waved for an imaginary second yellow card which Taylor did not produce.
Eight minutes later Wilshere beat Courtois with a thunderous left-footed strike from Rob Holding's pass.
Courtois continued to frustrate Lacazette and the Gunners were level when Bellerin caught Hazard, who converted from the spot.
Morata again should have scored after muscling his way past Mustafi but clipped the ball wide, leaving Antonio Conte to fall to his knees and pound the artificial grass in his technical area in frustration.
It was jubilation for Conte soon afterwards as substitute Zappacosta crossed and Alonso showed a poacher's instinct at the near post but fellow full-back Bellerin struck back with an even better finish.
There may have been one further late intervention, but Zappacosta hit the bar.