Substitute Leandro Trossard, a £27 million January signing from Brighton, scored his first Gunners goal on 66 minutes after fine work from Martin Odegaard and Bukayo Saka, but the home side were unable to hang on for a vital win.
After losing 1-0 at Everton last weekend, Arsenal were seeking a positive reaction but produced another underwhelming display as the visitors earned a deserved draw. They moved six points clear of Manchester City at the top but Pep Guardiola's side can cut the deficit in half with victory over Aston Villa on Sunday -- setting up Wednesday's clash when Arsenal and Man City face each other in north London.
1. Flat Arsenal open the door for Man City again
Arsenal got away with it last weekend, and have to pray they will do so again now. Manchester City failed to capitalise on Arsenal's 1-0 defeat at Everton last week as they lost at Tottenham but City have another chance to cut the gap at the top of the table after the Gunners dropped more points on Saturday.
In an interview earlier this week, Gunners captain Martin Odegaard suggested the club's training sessions had been among the best of the season as they looked for a reaction to defeat at Goodison Park. But Arsenal were curiously flat here against Brentford and only raised their game in moments during the second half.
City will host Villa on Sunday knowing victory will take them within three points of Arsenal, albeit having played a game more. Arsenal manager Mikel Arteta will be comforted by the cushion his team still enjoy, but questions about their durability in lasting the distance will only grow if they continue to allow their leads to erode like this.
Including the FA Cup defeat at City, Arsenal have now failed to win their past three matches. That hardly constitutes a crisis but the pressure is palpably building.
2. Brentford's Toney enjoys another "kickabout" against Arsenal
Brentford striker Ivan Toney and Arsenal have history.
When Brentford beat the Gunners at the start last season, Toney bullied the Arsenal centre-backs and tweeted about a "nice kickabout with the boys" -- a social media post which Arteta later used in his pre-match team talk ahead of the reverse fixture as motivation for his players. Alexandre Lacazette mimicked Toney's original Twitter post when Arsenal beat Brentford 2-1 in that second match.
Last season, Gabriel Magalhaes mocked Toney again when Arsenal won at the Brentford Community Stadium last season, a reaction the Bees striker described as "cringey."
Gabriel and Toney were reunited again here and the pair battled all afternoon, Toney fighting admirably and effectively to help Brentford carry a counter-attacking threat as Arsenal dominated possession. He missed two excellent chances, one in each half, before converting from close range to give Brentford the point their performance deserved, writing another chapter into a duel with more than a little edge.
3. Should Arteta shuffle Arsenal squad or stay the course?
Mikel Arteta has named the same starting line-up in every Premier League match since the World Cup. That run totals six matches, the first time the Gunners have done this for eight years.
The logic is clear: Arsenal have outperformed all expectations in ascending to the top of the table and Arteta wants to retain as much of that momentum as possible by rewarding the players who put them there. However, at the same time there have been signs of late that the team needs freshening up, having lost at Everton and now drawing against Brentford -- an issue underlined by a substitute scoring the home side's only goal.
However, Manchester City are up next at Emirates Stadium on Wednesday and facing their closest challengers presents a difficult conundrum for Arteta: freshen up the team or stick with the players that have outperformed City to this point?
Best and worst performers
Best: Ivan Toney, Brentford
Was a constant menace to Arsenal's back four and full value for his goal which earned the visitors a point.
Best: Bukayo Saka, Arsenal
Tried everything within his power to drag Arsenal to victory and produced an excellent cross for Trossard's goal.
Best: Ben Mee, Brentford
Organised Brentford's defence superbly, winning all five aerial duels and blocking two shots.
Worst: Gabriel Martinelli, Arsenal
Failed to create a single chance and was hauled off on 62 minutes when the game was goalless. The dip after such a fine start to his season continues.
Worst: Granit Xhaka, Arsenal
His more advanced midfield role has been a revelation for Arsenal this season but on Saturday he was largely ineffective.
Worst: Gabriel Magalhaes, Arsenal
Outfought by Toney in a manner rarely witnessed during the campaign to date.
Highlights and notable moments
Three weeks after Arsenal brought in Leandro Trossard from Brighton, the Belgian winger scored his first goal for the Gunners off the bench.
It took less than 10 minutes for Brentford to respond.
It won't win Ivan Toney a Puskas Award anytime soon, but the goal did net the Bees a big equaliser against the Premier League leaders.
After the match: What the managers said
Arsenal manager Mikel Arteta on the result: "Disappointed because we wanted the three points. We scored a goal, it was about controlling the direct play and set pieces and we didn't control one of those. Or we did, but we apply certain principles in defending because they apply certain rules but surely they didn't apply those rules."
Arteta on the Premier League race: "Everybody is suffering to win games. Games are won in margins in this league and when you take the margins away it becomes really difficult. The team had a really strong performance again today but we didn't get the three points."
Arteta on the need to rotate players: "You always think about that and with a few players especially when you lose. I'm delighted with how the boys tried and how much they wanted."
Brentford manager Thomas Frank on the result: "Ah, I'm more pleased with the performance. Wow, what a performance. I asked them to perform potentially the best of their season and I think we were up there. We can celebrate that. We didn't get three points but we can celebrate the performance. It was even more impressive the way we came back."
Arsenal: The Gunners stay home for a huge top-of-the-table clash on Wednesday against Man City, who sit in second and have been nipping at Arsenal's heels in the Premier League race. That match is at 2:30 p.m. ET on Feb. 15.
Brentford: The Bees get to rest for the coming week until they host Crystal Palace at 10 a.m. ET on Saturday, Feb. 18 in Premier League action.