Following a frenetic opening period in the first-leg of the Champions League last-16 clash, the hosts took a deserved lead after 11 minutes when Lukasz Fabianski pushed Silvestre Varela’s low cross into his own net.
However, Arsenal rallied and restored parity seven minutes later when Sol Campbell, making only his second start for the club since returning in January, nodded home from close range.
The Emirates Stadium outfit appeared set to take control of the tie after the break and Tomas Rosicky saw a penalty claim waved away moments before the game’s turning point in the 51st minute.
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Fabianski opted to scoop up Campbell’s low back-pass, giving referee Martin Hansson no choice but to award an indirect free-kick.
And, with Arsenal dallying, the kick was prodded quickly into the path Falcao who slotted home with ease from 12 yards.
On the touchline, Wenger was clearly furious and, after the game, the Frenchman explained why.
"You can never defend an indirect free-kick like that,” he said.
“The referee should have given us time to get a wall. You cannot let the players play like that.”
Immediately after the goal was given, Wenger was seen remonstrating with Hansson but the manager revealed that the referee remained tight-lipped over the incident.
"I do not know [why the goal was allowed to stand], he did not tell me," Wenger said. "You should ask him."
But, despite Wenger’s anger at the decision, the manager stopped short of saying he felt 'cheated'.
"I do not want to go into big stories about that,” he added.
“I do not understand his decision."
