Two errors from Arsenal goalkeeper Lukasz Fabianski allowed Porto to establish a 2-1 lead in the first leg of their Champions League last 16 tie here on Wednesday.
The 24-year-old Pole started in place of the injured Manuel Almunia but gifted the hosts an early lead with a soft own goal and presented them the opportunity to score their second five minutes into the second period by inexplicably picking up a back-pass.
The industrious Falcao was the beneficiary on the latter occasion, rolling the ball past a stranded Fabianski after Ruben Micael took a quick freekick to secure a slim advantage for his side prior to the second leg on March 9.
“Schoolboy goals. What can you do? Nothing. After the second goal, we went down,” said Arsenal captain Cesc Fabregas.
“We are still a little bit soft in that aspect. When we concede a goal we are not strong enough to lift ourselves up. Until the second goal we were having a very good game.”
Fabianski's nightmare performance distracted attention from an impressive return to European action by Sol Campbell.
The 35-year-old veteran marked his first appearance in continental competition since his return to the club in January by scoring the equaliser - three years and nine months since his goalscoring turn in Arsenal's defeat by Barcelona in the 2006 Champions League final.
Porto's winner sparked a furious reaction from Arsenal coach Arsene Wenger, who was also without William Gallas, Alex Song, Andrey Arshavin, Eduardo and long-term absentee Robin van Persie due to injury.
Wenger stormed to the touchline to remonstrate with Swedish referee Martin Hansson, who was in charge of his most high-profile match since the infamous Thierry Henry handball incident during the 2010 World Cup play-off between France and the Republic of Ireland.
Bayern Munich sink Fiorentina
Bayern Munich snatched a last-gasp 2-1 win over defiant Fiorentina in their last-16 first leg tie on Wednesday with a Miroslav Klose goal which both coaches agreed was several metres offside.
The controversy surrounded Klose's 89th minute header overshadowed Bayern's achievement in notching their 13th successive win in all events. Fiorentina were hanging on grimly when Arjen Robben's drive was parried by Fiorentina goalie Sebastien Frey.
The ball fell to Ivica Olic, who headed on for Klose to score with another header. The Italians protested to the linesman after Norwegian referee Tom Henning Ovrebo allowed the goal to stand and Juan Vargas was booked for dissent.