Arsenal's title hopes took a hit as they once again threw away a two-goal lead, this time against West Ham in a 2-2 draw.
Gabriel Jesus and Martin Odegaard scored clinical finishes to put Arsenal ahead after just 10 minutes but Said Benrahma's penalty pulled one back for West Ham just before half-time.
Arsenal had a chance to extend their lead early in the second half when they were awarded a penalty for Michail Antonio's handball, but Bukayo Saka missed the spot kick.
This proved costly as West Ham equalized just two minutes later through Jarrod Bowen's smart finish.
The dropped points could have major implications for Arsenal's title hunt, as they are now only four points clear of second-placed Manchester City, who have a game in hand.
After seeing Manchester City score three goals in the first half against Leicester, Arsenal responded with a fast start of their own.
Odegaard, Partey, Saka, and Ben White combined to release the latter down the right byline before he squared to Jesus for a simple tap-in.
Four minutes later, Martinelli's superb ball found Odegaard at the back post, who slammed home past Lukasz Fabianski.
Arsenal then sat on their two-goal advantage, failing to create many other clear-cut chances and enjoying over 75% of the ball as the half went on.
Arsenal invited West Ham back into the contest after a slack play by Partey, who was outplayed by Declan Rice. Rice quickly found Paqueta in the box. Gabriel brought the Brazilian midfielder down, and Benrahma cooly slotted the penalty home as West Ham ended the half in the ascendancy.
Both sides showed some impetus going forwards in the opening minutes of the second half. Martinelli's shot hit Antonio's outstretched arm in the box, and Arsenal was awarded a penalty.
However, Saka missed the target, and the significance of that miss was amplified two minutes later when Bowen scored.
The dropped two points, to go with the two dropped at Liverpool last week, could prove costly for Arsenal in the title race.
Mikel Arteta admitted that Arsenal only had themselves to blame after throwing away their second two-goal lead in a week.
"Fatigue-wise? No," he said in his post-match press conference. "What we produced in the first and second half against Liverpool was similar and today we put a higher input in the second half than we did in the first half.
"We were slower in everything that we did. I don't think the team is fatigued or looked fatigued. The best way to do it is convince them how good they are and do what they have to do."
With Manchester City in hot pursuit, Arsenal can ill afford any more slip-ups if they are to win their first Premier League title since 2004.
The result means that Arsenal are now only four points above second-placed Manchester City, who have a game in hand.
Arsenal's next match against Southampton will be crucial, as they look to extend their lead at the top of the table before facing Manchester City in a crucial game for the title race.