Guardiola’s side initially took control at the Emirates Stadium, with Joško Gvardiol seeing an effort cleared off the line by Declan Rice and Nathan Aké firing over before Arsenal had shown any signs of settling.
Even with the Gunners’ defiance in their effort to end a run of 12 PL H2H defeats, a nervousness remained early on that was epitomised by David Raya, who was fortunate to see the ball hit the side netting when his attempted clearance was blocked by Julián Álvarez.
After Eddie Nketiah cut inside Rúben Dias and curled an effort wide, the Gunners undoubtedly held their own in what had become a battle as the half progressed.
The home faithful were still left furious due to Mateo Kovačić being on the pitch following tackles on Martin Ødegaard and Declan Rice - picking up a yellow for the first of those.
Even so, having come closest to scoring a goal at the beginning of the half, Gvardiol came within a whisker of creating one towards its end with a cross that narrowly evaded Erling Haaland.
There was no Bukayo Saka in the Arsenal squad, but Martinelli made his return from the bench at HT and immediately added energy for the hosts, running outside Dias and hitting a strike to test Ederson.
The match soon quietened down again, which resulted in the two managers making triple changes seven minutes apart with a vital win on offer for the side that could find an extra gear.
It was Arsenal who reaped the rewards, as Martinelli’s shot cannoned off Aké to wrongfoot Ederson and nestle in the back of the net and secure a huge victory for the Gunners.
Arsenal’s unbeaten start to the PL season continued, joining North London rivals Tottenham Hotspur on 20 points, although they trail on goals scored.
Man City, meanwhile, have now lost back-to-back away league games for the first time since February as they were beaten in a league match by Arsenal for the first time since December 2015.
Flashscore Man of the Match: William Saliba (Arsenal)
