Hector Bellerin's first Premier League goal since January 2018 rescued a point for 10-man Arsenal, who fought back twice to secure a 2-2 draw at Chelsea despite having David Luiz sent off on his return to Stamford Bridge.
The Gunners' chances were dealt a severe blow midway through the first half when Luiz was sent off after taking out Tammy Abraham when he was through on goal after Shkodran Mustafi's woeful backpass.
Jorginho made no mistake from the penalty spot to give the hosts the lead going into the break, but the Gunners hit back early in the second half through Gabriel Martinelli, who took advantage of N'Golo Kante's slip to score his 10th goal of the season.
Chelsea thought they had nicked all three points when Cesar Azpilicueta bundled the ball home with six minutes remaining, but Arsenal leveled again just three minutes later through Bellerin to keep their slim chances of a top-four finish alive.
- Mikel Arteta proud of Arsenal spirit
- Premier League Table | Fixtures | Top scorers
- How the teams lined up
A point keeps Frank Lampard's side fourth, six points clear of fifth-placed Manchester United, who play Burnley on Wednesday. Meanwhile, Arsenal stay 10th, 10 points behind the Blues.
How the 10-man Gunners rescued a point...
Chelsea had Arsenal on the back foot from the very first whistle and the visitors needed a last-ditch block from Mustafi to keep out Mateo Kovacic's goal-bound shot in the seventh minute.
Andreas Christensen then nodded well wide from a corner and Tammy Abraham saw a header saved by Leno from close range, before Callum Hudson-Odoi's attempted cross clipped the crossbar after almost catching Bernd Leno out as the Blues' dominance continued
Chelsea: Arrizabalaga (5), Azpilicueta (7), Rudiger (6), Christensen (6), Emerson (7), Kante (6), Jorginho (7), Kovacic (6), Hudson-Odoi (7), Abraham (6), Willian (6).
Subs: Barkley (5), Mount (6), Batshuayi (n/a).
Arsenal: Leno (7), Bellerin (7), Mustafi (4), Luiz (5), Saka (6), Torreira (7), Xhaka (8), Pepe (6), Ozil (5), Martinelli (8), Lacazette (7).
Subs: Guendouzi (7), Holding (n/a), Willock (n/a).
Man of the match: Gabriel Martinelli.
In the end, it was a moment of madness from Mustafi that gifted Chelsea the lead, and a numerical advantage.
The German's under-hit back pass left Leno stranded on the edge of his own penalty area as Abraham rounded the Gunners goalkeeper. With the England forward about slide the ball into an empty net, Luiz bundled him down from behind to receive his marching orders.
After lengthy protests from the visitors, the Brazilian slowly made his exit from the field, much to the delight of the home fans, and Jorginho slotted home the spot-kick to leave the Gunners with a mountain to climb.
Despite Chelsea's dominance on the ball, the Gunners found a way back into the match when Martinelli kept his composure on a rare Arsenal breakaway.
The 18-year-old capitalised on Kante's slip on halfway before racing through on goal and calmly slotting the ball past Kepa Arrizabalaga to bring his side level.
Alexandre Lacazette soon had the ball in the net again as the 10-man Gunners went for more than just a point, but his strike was correctly ruled out for a clear offside.
Emerson Palmieri slotted into Chelsea's starting line-up in place of Reece James to face Arsenal in the Premier League clash at Stamford Bridge. James picked up a knee injury in the 1-0 loss at Newcastle and had been doubtful heading into the Tuesday night clash.
Mateo Kovacic started ahead of Mason Mount in the only other Chelsea change, while fit-again Hector Bellerin returned as captain for Arsenal, with Ainsley Maitland-Niles dropping out.
Azpilicueta then popped up in the penalty area to sweep home from close range for what he and his side thought was the winner, but the Stamford Bridge celebrations were cut short when Gunners captain Bellerin drilled home into the bottom corner to seal a point.
What the managers said…
Chelsea boss Frank Lampard: "I am disappointed given the situation of the game. We completely deserved to go 1-0 up. For a little bit after that, we were getting used to them with 10 men. But we created enough chances in the second half, it was just the same old story, we couldn't take them. In football, basic errors can cost you points."
Arsenal head coach Mikel Arteta: "Time will tell if this is a stepping stone, but at least I saw a reaction. I demand from the players that they never give up, we have to keep playing with the spirit we showed in every game. I'm proud of the way they reacted. They stepped up - if a team-mate makes a mistake, they have to have their back. It's a good point in the end."
Man of the match - Gabriel Martinelli
Gabriel Martinelli's equaliser was his 10th goal in all competitions this season, making him the first teenager to reach double figures in a single season for Arsenal since Nicolas Anelka in 1998-99.
The Brazilian youngster is a real bright spot for the Gunners so far this season and Arteta was full of praise for the 18-year-old.
"He is a great kid," Arteta said after the game. "He gets in the box. He plays against Cesar Azpilicueta who is one of the best defenders in the league and keeps taking him on. That is not easy."
How the Gunners celebrated Martinelli's equaliser...
Martinelli's equaliser sparked wild celebrations from the Arsenal players...
- Arsenal had just two shots in this game, scoring with both of them.
- The Gunners have been shown more Premier League red cards against Chelsea than they have vs any other side in the competition (8).
- Jorginho's penalty saw him become the first Chelsea player to score home and away against Arsenal in the same Premier League season since Juan Mata in 2012-13.
Chelsea travel to Hull City on Saturday for their FA Cup fourth-round clash; Kick-off 5.30pm.
Arsenal are also in FA Cup fourth-round action when they travel to Bournemouth on Monday, January 27; Kick-off 7.45pm