Porto introduced a player called Hulk last night, prompting thousands of comic-book roars around the Emirates Stadium, but it was Arsenal’s split personality, the transformation from sloppy to sublime, that offered the real intrigue. Derided for their careless attitude against Hull City at the weekend, they responded with a rampant win over Porto that featured two goals apiece from Robin van Persie and Emmanuel Adebayor and might have contained many more. Champions League group G is theirs to dominate.

The rush of goals and the attacking flair seemed on the surface to deepen the mystery of that loss to Hull, but there was a common thread in the defensive vulnerabilities exposed by their opponents in the first half. Though infrequent, Porto’s every counter-attack was enough to induce a wave of panic right around the Emirates. Issues of height of the Arsenal defence will continue to be debated by the supporters just on account of one Porto corner that bounced around the home side’s penalty area until, eventually, Gaël Clichy cleared off the line.

Arsène Wenger admitted that his team were striving to find the right balance between defence and attack at home, an issue less problematic on the road, when the onus to set the tone is not on his young cavaliers.

Even as the goals flowed at such a rate that Wenger could laugh as his players tripped over the ball in their eagerness to walk in a fifth, it was impossible to declare Arsenal a model of consistency. They travel to Sunderland on Saturday and any predictions — a return of the jitters or a mesmerising triumph? — are risky.

The drastic action from the manager that was expected in the wake of the chastening weekend defeat did not materialise, with Emmanuel Eboué the only casualty, making way for Samir Nasri. Wenger hoped that a sense of embarrassment would perk up the others and, although the first half-hour included a couple of notable scares, there was a marked sense of players needing to redeem themselves.

As an appetiser to the rush of goals, Theo Walcott had a shot pushed into the side-netting, Van Persie drew a good save from Helton and then volleyed over the crossbar from a sublime pass over the top by Cesc Fàbregas.

The 21-year-old schemer was incessantly picking holes in Porto’s erratic defence (Arsenal’s failings suddenly looked comparatively mild) and, inevitably, the Spaniard was involved in the opening goal on the half-hour, sliding the ball through to Adebayor, who was onside by inches. The Togo striker seemed to spend an age in thought, as if unsure of what to do next. In fact, he was astutely waiting for Van Persie. The Dutchman’s dash to the near post invited the cut-back and, with a poke of the left foot, it was 1-0.

The second was not far behind, Van Persie’s corner flying to Adebayor, whose downward header sprung up off the ground and in off the underside of the bar. With every goal came a tangible bolstering of self-belief.

As Van Persie took advantage of sloppy defending, cut into the penalty area and beat Helton with a low toe-poke into the bottom corner to add the third shortly after half-time, it was possible to believe that Hull truly was, as Wenger had hoped, “one bad day at the office” rather than a sign of anything more troubling. When Adebayor scored the fourth from the penalty spot, after Nicklas Bendtner was hacked down, winning football matches had never seemed so easy.

Up in the stands, Fabio Capello, the England manager, had a chuckle when the exciting Walcott missed a sitter and then Bendtner fell on his backside after being set up by the other substitute, Carlos Vela.

The home fans who had wailed at the weekend had their own laugh when Porto introduced Givanildo Vieira de Souza, registered with Uefa as Hulk, and offered their best impressions of Bruce Banner roaring. Make him angry? By then Porto were close to humiliation, but Wenger was wise to conclude that atoning for Hull will take more than one win, however restorative it appeared.

Arsenal (4-4-2): M Almunia - B Sagna, K Touré, W Gallas, G Clichy - T Walcott (sub: C Vela, 72min), F Fàbregas, Denilson, S Nasri (sub: E Eboué, 64) - R van Persie (sub: N Bendtner, 64), E Adebayor. Substitutes not used: L Fabianski, A Ramsey, M Silvestre, J Djourou. Booked: Clichy.

Porto (4-4-2): Helton - C Sapunaru, B Alves, Rolando, N Benítez - T Costa, R Meireles (sub: Givanildo Vieira de Souza, 64), Fernando (sub: Lucho González, 46), F Guarín - Lisandro López, C Rodríguez (sub: Candeias, 79). Substitutes not used: Nuno, P Emanuel, M Stepanov, Lino. Booked: Costa.

Referee: H Fandel (Germany).