Newcastle striker Alexander Isak dented Arsenal's title hopes as his bullet header condemned them to a second Premier League defeat of the season.
The Sweden international converted Anthony Gordon's inviting 12th-minute cross with aplomb to claim his third goal in as many games and hand the Magpies a 1-0 win in front of a crowd of 52,249 at St James' Park.
Three points were just reward for a committed display which kept the Gunners at bay despite the wealth of possession they enjoyed, and provided further proof that Eddie Howe's men, for whom full-backs Lewis Hall and Tino Livramento were outstanding, are emerging from the patchy form which characterised their early-season performances.
Arsenal counterpart Mikel Arteta will have been happy with much of what he saw ahead of Wednesday night's Champions League trip to Inter Milan, but a lack of incision and pace in his team's play ultimately cost them dearly.
The Gunners, who lost on Tyneside in controversial circumstances last season, set off as if they meant business with Leandro Trossard dragging a second-minute shot wide of Nick Pope's goal, and former Magpie Mikel Merino was spectacularly wayward with an ambitious seventh-minute volley.
Bukayo Saka dragged an 11th-minute attempt wide of the near post after Jurrien Timber had been allowed to control keeper David Raya's long ball straight down the middle, but the momentum shifted dramatically within seconds.
Gordon, lining up on the right of the front three rather than his preferred left, crossed first time when presented with the opportunity to do so and Isak rose between central defenders William Saliba and Gabriel to head firmly past Raya.
Saka headed wide under pressure from Hall, but Newcastle were easing their way into the game and enjoyed a sustained period of pressure which ended when Bruno Guimaraes' shot was deflected into Raya's arms.
Gordon saw a 24th-minute cross fly dangerously across goal after running on to Joe Willock's fine ball around the corner, but Fabian Schar had to hack away Thomas Partey's ball from in front of his own goal as Arsenal responded.
Schar and Hall combined to block Merino's shot after Saliba had headed down the resulting 27th-minute corner with the temperature in an already competitive encounter rising all the time.
Arsenal old boy Willock almost returned to haunt his former club when he exchanged passes with Gordon before forcing a save from Raya within seconds of the restart, but with both sides careless in possession, the game became increasingly scrappy.
The visitors continued to enjoy a greater share of the possession, but lacked the penetration to hurt the Magpies, and Willock might have doubled their advantage with 58 minutes gone when he fired over after being played in by Joelinton.
Raya had to beat away Isak's dipping 64th-minute strike, but Pope was relieved to see Declan Rice's shot deflected wide of his far post by Schar with the visitors redoubling their efforts.
Hall made a vital 68th-minute block after Trossard had stabbed Rice's corner back across goal and Joelinton planted an 87th-minute header into Raya's grasp, but it was Rice to whom the final chance fell four minutes into stoppage time, only for him to head Saka's far-post cross wide.
