By the end, it had begun to feel like an illusion that this is an Arsenal side looking down from the top of the Premier League. Manchester City, looming in their wing-mirrors, had made them look ordinary, in keeping with every team that has visited their ground in the league this season. Eight games, 35 goals – and now a full-on dismantling of the side that boasted the best defensive record in the league before this game.

Arsenal can console themselves that Manchester United endured their own ordeal here in September, and Tottenham suffered even worse when they were hit for six without reply in November, but it was still a deeply chastening experience for Arsène Wenger's team. Arsenal's manager said he did not want to use their midweek Champions League tie in Naples as an excuse, but then proceeded to do exactly that. Title-winners generally do not cite fatigue midway through December and Wenger was stretching the truth to the point of incredulity when he argued Arsenal might have extended their lead over City to nine points rather than being cut back to three.

City, he said, were "not unbeatable" on that performance, adding that Everton and Southampton had been just as good. A more realistic appraisal is that Arsenal were outplayed and finished in near disarray, with Jack Wilshere risking a ban for showing his middle finger to the home crowd and Per Mertesacker angrily remonstrating with Mesut Özil for not applauding the away fans; the midfielder later apologised for the omission. Maybe it could be put down as merely a one-off. But Arsenal, put bluntly, did not look like champions‑in-waiting, or even close.

City, in stark contrast, have maintained their immaculate home record, averaging better than four goals per game. Pellegrini was still not fully satisfied, on the basis they had conceded more goals in one match than the previous seven fixtures at this ground. Yet the more relevant fact is that on each occasion Costel Pantilimon picked the ball out of the net it was out of keeping with the natural pattern of the game. Arsenal scored three – but each time it came as a jolt.

If there was a downside for City, it was that Sergio Agüero limped away early in the second half with a calf injury. Agüero had opened the scoring, cracking in a wonderful, scything volley after a corner had skimmed off the head of Martín Demichelis. It was his 19th goal in 20 appearances and he would be a considerable loss if the injury affects him over the Christmas programme.

All the same, there was plenty to encourage City about their chances of catching, then overhauling, Arsenal in top position. Fernandinho, with his first City goals, played what Pellegrini described as "the perfect game". Yaya Touré was magnificent, bar an uncharacteristic mistake for Arsenal's first goal, and David Silva demonstrated why there was a banner inside the stadium reading: "Silva es Magico".

If anything, Arsenal were a touch fortunate bearing in mind the two chances Álvaro Negredo missed from good positions in the opening half. The first one said a lot about the home side's performance, created by a lovely piece of skill from Vincent Kompany followed by a perfectly placed through-ball off the outside of his right boot. For City, it was that kind of day.

Arsenal looked just as Wenger had feared: leggy, with little zip to their passing and only a brief passage of play, at 1-1, when they showed any real control. Even then, there was a slice of good fortune attached to Theo Walcott's goal. Touré, of all people, was guilty of losing the ball inside his own half. Aaron Ramsey fed Özil on the left and, almost in slow motion, Walcott's shot bobbled past Pantilimon from 20 yards. The goalkeeper looked awfully flat-footed and, in terms of his personal contest with Joe Hart, it was not the only occasion he appeared vulnerable.

Touré quickly set about making amends and it was a beautifully weighted pass off the outside of his boot that helped City regain the lead. Pablo Zabaleta was surging forward from his right-back spot and Negredo turned in the cross from close range.

Wenger talked about his side committing "easy mistakes" and he might easily have been referring to Özil's carelessness before the goal that made it 3-1, playing a senseless pass to Mathieu Flamini, then watching Fernandinho steal in to bend a wonderful shot beyond Wojciech Szczesny.

Soon afterwards, there was another moment that typified Arsenal's performance. Olivier Giroud, who looks exhausted, could have set up Walcott with a simple sideways pass but got his feet horribly wrong and miscued it straight out for a goal-kick. Arsenal then thought they should have had a penalty for Zabaleta's handball, although the ball struck his thigh first. Wenger's view was that the referee, Martin Atkinson, had "a bad game" and he also complained, justifiably, about some poor offside decisions. Yet the imbalance between the teams was so great it seems unwise to dwell too much on these points.

Walcott's curling shot into the top corner was a lovely finish for 3-2 but incongruous with the rest of the game and it was three minutes later that Jesús Navas, Agüero's replacement, crossed for Silva to flick in a shot and restore their two-goal advantage.

For the next goal, it was Wilshere's turn to lose the ball in his own half, Fernandinho and Samir Nasri exchanging passes before the Brazilian dinked his shot over Szczesny. Mertesacker's header for Arsenal's third felt like another deception on a day when Arsenal also lost Laurent Koscielny to a gashed knee. Then in stoppage time Szczesny brought down the substitute James Milner and Touré's penalty made it the first time since 1937-38 that City had scored six at home on three occasions.

That, funnily enough, was a relegation season. This time around, they are going to take some stopping at the right end of the league.