Arsenal missed the chance to re-establish their six-point lead at the top of the Premier League as an impressive Brentford side held them to a 1-1 draw.
After seeing second-placed Manchester City sweep Fulham aside on Wednesday, Arsenal's lead at the top was trimmed to just three points - but the Gunners could only improve that margin by one on a difficult night in west London.
The Gunners did not have a shot on target in the first half, despite Gabriel going close from an early corner. It was Brentford who had the best chance of the half as Igor Thiago's header from 12 yards was superbly kept out by David Raya.
Arsenal brought on captain Martin Odegaard - back from injury - at half-time for the disappointing Eberechi Eze and that made a difference, with the league leaders then taking the lead from their first effort on target.
Just as Bukayo Saka was ready to join the action, Noni Madueke headed Piero Hincapie's fierce cross into the far corner.
But Brentford were not disheartened by going behind, if anything it spurred them on. Keane Lewis-Potter should have levelled but put a free header wide from a corner.
At the other end, Michael Kayode put in a brilliant last-ditch tackle to stop Viktor Gyokeres from making it two, when Declan Rice should have shot earlier.
And those two Brentford players had a role in the equaliser. Kayode's long throw was flicked on at the near post, with Lewis-Potter beating Odegaard to the ball at the far post to level.
And Brentford were not done there - as they looked close to getting a second over Arsenal. Gabriel avoided a second yellow card for a high challenge on Dango Ouattara, with Raya tipping the resulting free-kick over.
Then came a big moment as Thiago broke clear for a one on one - only for Cristhian Mosquera, deputising for the ill William Saliba - to deny him with a strong tackle. Rice put in a similar last-ditch block to stop another Ouattara-led breakaway.
Neither side could get a winner, in a result which boosts Brentford's European hopes - and damages Arsenal's challenge.
Arsenal manager Mikel Arteta:
"We had a massive chance in the end, one v one for Gabriel Martinelli but it wasn't meant to be.
"We have to do our job and come to all these places like the rest of the teams. You have to be at your best every game and have the luck as well you need in games to conquer the three points each week.
"We started the second half really well, the first 20-25 minutes.
"They score the goal and from there we lacked more composure to maintain the goal better, play in the right areas, to instill more discipline.
"Because we started to give a lot of unnecessary free-kicks away and bad clearances and allow the ball in the channels and they start to generate set-pieces - and they are really good at it, so credit to them as well."
Brentford head coach Keith Andrews:
"Inside the box today, I was really happy with our movement, with our body language.
"There's a lot made of Arsenal's set-pieces... we're not so bad ourselves.
"I thought we were excellent, brilliant in most aspects for most of the game against a top, top team with brilliant individuals.
"First half, the way we approached it, got control of the game, created better opportunities. Second half, Odegaard coming on changed the dynamics and how they play.
"They had control for 15-20 minutes but I thought we were excellent for the last 30 minutes and looked the team more likely to win."
Your Site' Dan Long at the Gtech Community Stadium:
"Those who doubted Keith Andrews have had to swallow their words. We are running out of superlatives for Brentford.
"A first ever win over Aston Villa at Villa Park was followed up by a first win at St James' Park since 1934, and now they have held Premier League leaders Arsenal to a 1-1 draw.
"Incredibly, they are most likely frustrated they did not come away from the game with all three points, given Igor Thiago had two huge chances - one in either half - to score his 18th Premier League goal of the season.
"Speaking in his press conference afterwards, Andrews referenced his side playing 'relentless football' and 'in a fearless manner'. It's hard to argue otherwise.
"Arsenal are a menacing team, particularly at the moment, but Brentford made them look ordinary at times. The Gunners managed just two shots on target and their xG totalled 0.6 - their third-lowest in a Premier League game this season.
"Like all managers, Andrews will not look beyond the next game - and he most certainly will not entertain talk of qualifying for Europe with 12 games still to play.
"But if the Bees keeping delivering results and performances like this, it is only a matter of time before he may have to."
