Arsene Wenger directed his anger at referee Martin Hansson for allowing Porto's winning goal, but Cesc Fabregas had it right when he described Arsenal's defending as "schoolboy" for both goals his side conceded.
All Arsenal's good work was undone by two horror moments at the back. In years gone by the Gunners' performances in Europe used to be founded on a solid, unshakeable defence. Not any more. Lukasz Fabianski, the rookie goalkeeper so highly rated by Wenger but not by anyone else, threw in the first goal when he was caught on the wrong foot by Silvestre Varela's low cross as early as the 11th minute. Then, in the second half, Sol Campbell and Fabianski contrived to allow Porto to score with the net unguarded.
Wenger was furious at Hansson, the man who failed to spot Thierry Henry's infamous handball in Paris when France got the better of Ireland in last November's World Cup play-off, but his defence only had themselves to blame. Hansson's decision to allow Porto to take an indirect free-kick inside the Arsenal penalty area was certainly the right one, even if it left Arsenal with no time to regroup.
The official was guilty only of sticking to the rules of the game. The one mistake he might have made was to stand in the way of Campbell as Ruben Micael passed for Falcao to score into the empty net. However Arsenal should not have been so distracted.
To rub salt into the visitors' wounds, Hansson also missed what looked like a clear penalty when Tomas Rosicky was fouled by Alvaro Pereira in the second half. Before the match Wenger had called on his team to deliver a "special" performance. This was not what he had had in mind. Arsenal began the game shakily. Campbell, back in Champions League action for the first time since the 2006 final, when Arsenal lost against Barcelona, looked every one of his 35 years when he was outpaced by Falcao in the second minute. Porto's Colombian striker set up Ruben Micael but fortunately for Arsenal Thomas Vermaelen was perfectly placed to block the shot on goal. Moments later Hulk shaved the upright with a low shot from 12 yards in a nervous opening for the visitors.
Things went from bad to worse in the 11th minute. Varela skinned Gaël Clichy down the Porto right, and his low cross appeared to be totally harmless until Fabianski, deputising for the injured Manuel Almunia, fumbled the ball over the line. Fabianski needed a decent performance to allay the doubts about his nerve after he messed up in last season's FA Cup semi-final defeat by Chelsea. This was not it. The Pole looked aghast as the Estadio do Dragao erupted. Tests of character do not come much greater than the one he faced last night.
Fortunately for Wenger, Campbell showed the leadership that convinced the manager to re-sign him during the January transfer window. Porto's lead lasted all of seven minutes, as Nicklas Bendtner won a corner. Fabregas floated a ball into the goalmouth, Vermaelen flicked the ball on, Rosicky headed back across goal and Campbell was there to force the ball into the Porto net. How he enjoyed it.
In one telling moment, Wenger's decision to give the veteran a second chance was vindicated. It was Campbell's 12th goal for the club on his 200th appearance, and his first since he scored in that 2006 final in Paris. The goal settled Arsenal who coped with a vibrant Porto side until a second defensive lapse in the 51st minute allowed the hosts to take the lead for the second time. Campbell touched the ball back to Fabianski who inexplicably caught it. The official correctly blew for an indirect free-kick which was quickly taken by RubenMicael to Falcao, who passed the ball into the empty net while Campbell took a breather and Fabianski had his back turned.
Porto could not believe their luck and mobbed Falcao. Wenger was furious on the touchline, and let the Swedish official have both barrels before the match could restart. Yet it was naïve defending by Fabianski, as one of the fundamental rules of goalkeeping is that you never turn your back on the action. However the punishment of conceding what could prove to be the goal that decides Arsenal's future in the Champions League far exceeded the crime of passing the ball back to the keeper.
Campbell's goal at least gives Arsenal an even chance of going through when the sides meet again in three weeks' time. The contest at the Emirates should prove to be a lively encounter as the ill feeling between the sides began to grow the longer the game went on.
The first half ended with an angry confrontation between both teams after Fabregas was twice hacked down in the space of a minute by Ruben Micael. The Spaniard refused to shake hands and Nasri also got involved as tempers began to fray, and the Arsenal assistant manager Pat Rice had to intervene to lead his players down the tunnel.
Campbell is unlikely to be in the side for the return leg, as William Gallas is expected to have recovered from his calf strain by then and surely he will be recalled to take his place alongside Vermaelen at the centre of defence. Campbell's performance last night was not a perfect one but considering he started the season playing for Notts County in League Two, it was a remarkable display by the veteran and one that fully justified Wenger's decision to give him the chance to resurrect his Arsenal career.
Porto (4-3-3): Helton; Fucile, Rolando, Bruno Alves, Pereira; Ruben Micael, Fernando, Raul Meireles (Costa 67); Varela, Falcao, Hulk. Subsitutes not used: Beto (gk), Guarin, Belluschi, Mariano Gonzalez, Maicon, Lopes.
Arsenal (4-2-3-1): Fabianski; Sagna, Campbell, Vermaelen, Clichy; Denilson, Diaby; Rosicky (Walcott 67), Fabregas, Nasri (Eboue 88); Bendtner (Vela 83) Substitutes not used: Mannone (gk), Ramsey, Silvestre, Traore.
Referee: M Hansson (Sweden).
Man-for-man marking, by Steve Tongue
Lukasz Fabianski Oh, what a night. Flat-footed for Varela's cross to continue the tradition of own goals by Arsenal goalkeepers, then thoughtlessly handling Campbell's backpass for the second goal. 3/10
Bacary Sagna More solid than his full-back partner, which was just as well. Ever ready to venture forward as well, though without much reward. 6
Sol Campbell Not a man for fairy tales but was enjoying one for 50 minutes until the second goal. Superb early tackle on Falcao before heading the equaliser. 7
Thomas Vermaelen For all Arsène Wenger's protestations about that second goal, was caught dreaming. Not as sure-footed as in his impressive first half of the season, though still a threat at set pieces. 6
Gael Clichy The young Frenchman is having a bad patch and getting caught out of position. Varela went past him for the first goal as easily as Nani for Manchester United did recently. 5
Abou Diaby Unable to create much, he dropped deeper, either involuntarily or under orders. Put in some strong challenges and was booked for a foul on the lively Varela. 6
Denilson Should have felt at home among all the Portugese and Brazilians. Some neat work without ever taking control of midfield. 6
Cesc Fabregas The young captain is having to take an awful lot on himself on days like these, not least because he has become a target for unscrupulous opposing players. 7
Tomas Rosicky Decent performance from a player who is not a natural winger. Set up Campbell's goal with his header and deserved a penalty early in the second half. 7
Nicklas Bendtner Provided something different with an aerial threat among all the dainty ball-players. Some good attempts including a back-header and fierce drive. 7
Samir Nasri Stationed wide on the left, found it harder to become involved in the game than some of the other midfielders. Replaced after tiring. 5
Theo Walcott (replaced Rosicky, 67). Worked hard on both flanks. 7
Carlos Vela (replaced Bendtner, 82). Little chance to impress. n/a
Emmanuel Eboue (replaced Nasri, 87). Late sub. n/a