They made it look too easy too soon. Ahead on away goals after 11 minutes, Arsenal took the aggregate lead in the tie after 27 and from there the outcomewas rarely in doubt.
It will lead to the casual dismissal of this task, despite the mammothmargin, as if Porto regularly surrender the second leg of Champions League ties so spectacularly.
Make mine a double: Nicklas Bendtner wheels away after firing his second of the evening
In fact, they had not lost in 24 Europeanties in which they had won the first leg at home, and Arsenal had not progressed after losing a first leg in Europe since eliminating Hajduk Split of Yugoslavia (now Croatia) in 1978.
This was no mean feat, however comfortableit will have appeared.There is a long way to go, but could it be that Arsene Wenger's players are at last drawing strength from adversity?
It would be good to think so. Two years ago, the injury to Eduardo cast a pall over their season. Some teams are inspired by such anguished moments.
They pull together against the odds, grow a hardened shell. Arsenal, too often, project the victim mentality. They appear brow-beaten, put upon. Perhaps that is why opposing teams regard them as a soft touch, and seek to bully them all the more.
Spot on: Nicklas Bendtner completes his hat-trick from the spot
The injury to Aaron Ramsey would appear to have had the opposite effect. On the day, at Stoke City, it provoked a late revival and a win. Then, three goals were put past Burnley, and it could have been more.
Last night, without Cesc Fabregas and William Gallas, the vocal leaders of the club, Arsenal were inspired. It is easy for players to don the shirt of a stricken team-mate and to make an empty pledge that success will be achieved in his name.
Events on the pitch matter more than words or gestures.The crowd sing Ramsey's name loudly but it is the way the players are carrying the season forward that counts.
Amazing: Nasri caps a wonderful run with Arsenal's third goal
He is gone for now, but certainlynot forgotten.There will be tougher nights than this, of course, less fragile opponents than Porto, whose record in Europe belied a truly atrocious defence of their first leg lead.
There were moments in which the tie could have turned, a Falcao chance and a Samir Nasri clearance off the line, when Arsenal led 2-0 that caused more than a flutter around the stadium.
Yet, at the opposite end, Porto's calamities were too much to overcome. Fucile, the right back, in particular, had a game that brought to mind the experienceof Arsenal understudy goalkeeperLukasz Fabianski in Portugal two weeks ago.
For the first goal, he took out his goalkeeper,Helton, yet left Andrey Arshavin and Nicklas Bendtner unmolested; for the second he passed straight to Arshavin who set up Bendtner again, and his foul on Emmanuel Eboue gave Bendtner his penalty third.
Only Cristiano Ronaldo is now ahead of him in this season's Champions League goalscoring charts. Bendtner tops the list of players in second place with four goals having played just 272 minutes.
Wenger deadpanned that he hoped his first hat-trick would give him more confidence, the gag being that Bendtner's self-regard would make the kids from Fame appear inhibited.
Bendtner is one of those players on whom Wenger's reputation rests. Wenger used to be the manager who proved everybody wrong, who plucked a young player from the fringes of the squad, fast-tracked him through the Carling Cup and into the starting XI and then defied those who called it a gamble.
Mastermind: Arsene Wenger
And, usually, he was right. Then things changed.Arsenal stopped winning trophies and Wenger's judgments grew increasingly shrill and at odds with the evidence.
He said Philippe Senderos was a world class central defender, he gambled on not missing Mathieu Flamini from the heart of midfield, and he stuck with Bendtner, although of late more through necessity.
In the land of the blind the one-eyed man is king, and in a land without a fit centre forward, the Danish bloke with a No 52 on his back because he needed that many chances to score, gets a run-out in the Champions League.
Except, last night, Bendtner appeared as Wenger sees him. His were not brilliant goals, but they were match defining and, in the circumstances as beautiful as any 30-yard Arjen Robben shot for Bayern Munich or mazy, Brazil-lite dribble like Nasri's to clinch this tie.
The sniffer's goal is much under-valued and that is what Bendtner scored. Gerd Muller never apologised for getting them, nor Alan Shearer nor Allan Clarke.
All Guns blazing: Emmanuel Eboue hit the Gunners fourth
It helps to have a player like Arshavin alongside, over the last year the most revelatory presence in the Premier League (unless we count this chap Wayne Rooney, who has gone from being Ronaldo's gofer to Manchester United's most dangerous attacker).
What Bendtner lacks in finesse, Arshavin has to spare. At times, with the ball at his feet, the moment freezes, as if all around are transfixed, wonderingwhat will happen next: usually something delightful.
So when he gets it wrong, it comes as something of a shock and, heavens, did Arshavin miss a sitter late in the first half.
Nasri cut the ball back from a tight angle, leaving the goal open, Arshavin moved on to the ball and then, inexplicably,provided the perfect tableau of how not to strike it: leant back, head up, open side-foot.
Schoolboy stuff really. Maybe he generously did not want to make it look too easy too early because, for a player of his class, doing that must have been very difficult, indeed.
Even harder than putting five past Porto, as it transpired.
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