The goal, in the end, that was decisive was scored two weeks ago -- or perhaps back in September. Had Pierre-Emerick Aubameyang not scored with 12 minutes remaining to give Borussia Dortmund a 3-1 win against Napoli last month, or had Juan Zuniga not scored a late own-goal in Napoli's 2-1 win over Dortmund on the first match-day, it would have been last season's Champions League runners up that went out and Rafa Benitez's team that went through.
As it was, a late goal for Dortmund, away to Marseille, meant it eked through as group winner. It meant that all Napoli's second-half heroics did were to ensure that it became the first side ever eliminated from the Champions League having collected 12 points in the group stage. And it meant that Arsenal went through not as a group winner, but in second place, thus facing a more treacherous final 16 draw.
"We're happy to be through," Arsene Wenger told Sky Sports following the result. "We took the game very seriously, prepared well, were well-focused. In the second half we dropped physically a lot with the game on Sunday [the 1-1 draw against Everton] but Napoli played very well tonight and we were a little but on the edge for some minutes but in the end we got through. When you win the group you feel you have done very well, when you come second you think you have just done the job and you hope for a good draw."
Arsenal's position really should never have been in doubt. For Napoli to go through it needed to win and, if Dortmund won against pointless Marseille, to win by three goals. It said much for the lack of hope among Napoli fans that the San Paolo was far from full, something that wasn't just down to delays caused to Arsenal's official buses by anti-hooligan measures.
The initial news from Marseille wasn't good for Napoli either, as Robert Lewandowski ran on to Eric Durm's pass and lofted his finish over Steve Mandanda after four minutes. But when Roman Weidenfelller misjudged Dimitri Payet's free-kick eight minutes later, Saber Khalifa headed against the bar and Souleymane Diawara nodded the rebound over the line. When Payet collected a second yellow card for simulation 11 minutes before the break, the game seemed up.
Yet Marseille, with nothing to play for but pride, produced a committed defensive display. It was against Napoli at the Emirates at the beginning of October that Arsenal first hinted that this might be a special season for it. In the first half hour that day, it was superb, playing kick possession football that left an in-form Napoli dancing after shadows. At the San Paolo, it was a much slower game that showed the other side of Arsenal's approach. Its passing has been sharper this season than in recent years but what it has really developed is a pragmatism.
It is able to withstand pressure these days, to hold an opponent at arm's length, to break up play when it needs to. In the first half at least, it spoiled, it won free-kicks -- something in which it was helped by Napoli's indiscipline, Dries Mertens and Blerim Dzemaili in particular repeatedly stretching for balls they had little chance of winning - and, every now and again, it put together skeins of passes that took periods out of the game. Laurent Koscielny was particularly impressive, always ready to stride forward from the back and become an extra passing option in midfield.
The one concern at half time was Wojciech Szczesny, who raced needlessly off his line when Christian Maggio was played in on the right, turning a crossing opportunity into a shooting one, and then tried a senselessly difficult chipped ball from a backpass that, fortunately for him, hit Gonzalo Higuain on the head and bounced out for a goal kick.
But the introduction of Lorenzo Insigne 12 minutes into the second half changed everything. He operated on the left, with Jose Callejon switching into the center in place of Goran Pandev and Napoli suddenly was energized. It was probably unfortunate that the first clear chance fell to Pablo Armero, rampaging forward from left back, and specifically to his right foot. Of his shot, scooped delicately into Szczesny's hands, the kindest thing to say is probably that he's very left-footed.
Arsenal, though, was rattled and the chances kept coming until, with 17 minutes remaining, Higuain turned on to Callejon's pass and struck a shot across Szczesny and into the bottom corner. With Dortmund still drawing in Marseille, Lewandowsi and Marco Reus having missed easy chances, that meant Napoli was in the box seat. When Arteta gathered a stupid second yellow card for a careless foul from behind on Callejon -- "very harsh" said Wenger - even the three-goal margin that would have taken it through in the event of a Dortmund win began to seem possible, and it was hard to avoid the thought that it might have begun the attacking surge rather earlier than it did.
"The most difficult football is when you are between two -- do we attack, do we defend?" said Wenger. "And as long as we didn't score a goal tonight, they had a chance. Maybe it helped a little bit that Dortmund was at 1-1 when we were down to 10 men and they played a little bit with the handbrake thinking they were through and that's why we didn't come under too much pressure at the end."
Lewandowski was denied a penalty when he seemed to be bundled over by Mandanda, but with three minutes remaining, the goal did at last come in the Velodrome. Julian Schieber laid back Henrykh Mkhitaryan's cross for Kevin Grosskreutz, whose shot, as he slipped, struck Mandanda's hand but crept in. That left Napoli needing to score two in around seven minutes.
It got one, as Callejon lofted Insigne's pass over Szczesny, but as Arsenal kicked off again the final whistle went.
Arsenal was through for the 14th consecutive season, but it might pay for its careless second half in the forthcoming draw. Dortmund, meanwhile, as it did so often last season, found a late goal when it needed it. It may have scrambled through, but when its injured players are back, it remains a force.