Arsenal dropped points in the Premier League for the second week running after they were held to a 1-1 draw by Brentford.
Thomas Frank's Bees maintained their marvellous big game record this season with a deserved point at the Emirates Stadium.
Manchester City can close the gap on Arsenal to three points on Sunday should they beat Aston Villa.
Brentford should have taken a fifth-minute lead on the counter attack when Ivan Toney's low cross was met by Rico Henry, whose shot from six yards sailed wide with a touch off of Aaron Ramsdale.
The hosts saw the majority of the ball and carved out a half-decent opening after the Bees failed to clear a corner, with Oleksandr Zinchenko half-volleying over from just inside the box.
Bryan Mbeumo had the ball in the net in the following minutes after muscling Gabriel Magalhaes off the ball to reach a Toney header, slotting in at Ramsdale's near post, but the goal was chalked off as the Cameroonian was adjudged to have committed a foul on the centre-back.
Arsenal were furious that they were denied a penalty when Henry clumsily brought down Bukayo Saka, but given the winger tried to honestly stay on his feet before going over, Brentford got away with the decision.
Toney then rattled the crossbar from close range after meeting Mbeumo's cutback before being denied by Ramsdale with a 25-yard dink as a fast but goalless first half continued.
The first sweeping move of the afternoon for Arsenal came shortly before the break. Ben White's deep cross was headed back by Granit Xhaka and volleyed just over the bar by Gabriel Martinelli.
Just after half-time, Saka switched to the left flank to try and catch Brentford napping, firing a shot towards the near post, only to be denied by David Raya.
Martin Odegaard was next to test Raya with an effort from inside the box as the Bees started to look a little more open defensively.
Some sloppy defending from William Saliba saw Toney flash another shot at goal, this time finding the side-netting.
But despite their many frustrations, Arsenal took the lead on 66 minutes. Saka's deep ball through the six-yard box was tapped in by substitute Leandro Trossard for his first goal in Gunners colours.
Their lead didn't last for long though, as Toney equalised seven minutes later. Arsenal failed to clear Mathias Jensen's free-kick from a wide area, and Christian Norgaard eventually managed hook it back for the striker to nod in from point-blank range.
Brentford managed to survive nearly ten minutes of stoppage time to claim their first ever point at the Emirates Stadium.
Arsenal player ratings
GK: Aaron Ramsdale - 4/10 - Needlessly committed to trying to beat Norgaard to the ball prior to Brentford's equaliser.
RB: Ben White - 5/10 - Provided little use at either end of the pitch.
CB: William Saliba - 3/10 - Manhandled by Toney in a role-reversal of the reverse fixture back in September.
CB: Gabriel Magalhaes - 5/10 - Was extremely fortunate that Mbeumo's early strike was ruled out for a soft foul.
LB: Oleksandr Zinchenko - 6/10 - Wasn't self-destructive and was decent in possession, unlike his defensive colleagues.
CM: Thomas Partey - 6/10 - Competitive in the midfield battle with Norgaard.
CM: Granit Xhaka - 5/10 - Played a little more like the Xhaka of old, making strange decisions under pressure.
RM: Bukayo Saka - 8/10 - Arsenal's shining light. Made life tough for Henry and unlocked the initial route to goal.
AM: Martin Odegaard - 5/10 - Couldn't quite pick the lock against a deep defence once again.
LM: Gabriel Martinelli - 4/10 - Easily snuffed out by Roerslev. Had no idea how to play his way out of double teams. Replaced by Trossard just after the hour mark.
CF: Eddie Nketiah - 5/10 - Struggled to stand out against another deep block.
Substitutes
Leandro Trossard (62' for Martinelli) - 8/10
Fabio Vieira (81' for Xhaka) - N/A
Manager
Mikel Arteta - 5/10 - Arsenal lacked their usual intensity and while bringing Trossard into the game helped change that, the hosts couldn't sustain that level.
Brentford player ratings
GK: David Raya - 6/10 - Made some decent saves and was useful in playing from the back.
CB: Kristoffer Ajer - 6/10 - Looked assured in his first big game since returning from injury.
CB: Ethan Pinnock - 8/10 - The man mountain lived up to his nickname. Cleared everything away.
CB: Ben Mee - 7/10 - Had to help Henry slow Saka down. Did most of his duties well.
RM: Mads Roerslev - 7/10 - Would have been a flawless performance had he not let Trossard evade him for Arsenal's opener.
CM: Vitaly Janelt - 6/10 - Provided the necessary grit in midfield.
CM: Christian Norgaard - 7/10 - Sloppy on the ball for the most part but grabbed a telling assist and was excellent defensively.
CM: Mathias Jensen - 6/10 - Wriggled his way out of tight holes and helped progress the ball.
LM: Rico Henry - 5/10 - Made to pay by Saka. Little lucky not to have conceded a penalty in the first half.
CF: Bryan Mbeumo - 7/10 - Caused all sorts of problems for Arsenal and did his bit defensively too.
CF: Ivan Toney - 9/10 - Got his revenge against Saliba after the Frenchman pocketed him earlier this season. Dominated their duels and grabbed a deserved goal.
Substitutes
Yoane Wissa (71' for Mbeumo) - 5/10
Josh Dasilva (71' for Janelt) - 6/10
Kevin Schade (90+6' for Toney) - N/A
Manager
Thomas Frank - 8/10 - The Dane said this week that Brentford would need to be at their best ever in order to leave Arsenal with something. They were very, very good indeed.
