Arsenal scored a 2-1 victory over Barcelona in the first leg of their final 16 match in February, stunning Guardiola’s men with two late goals to claim a narrow advantage.
However, the asterisk against that memorable night in north London is that Barcelona would have been out of sight by halftime had it not been for uncharacteristic profligacy by Messi and David Villa in an opening period where Arsenal’s defense was sliced open repeatedly.
The message Ferguson has been drumming into his players is that one lapse of concentration today could be fatal.
It was slack play that led to Barcelona’s early opening goal from Samuel Eto’o in Rome two years ago, setting United on the path to defeat.
“We lost the first goal due to that sudden lapse of concentration, that was what cost us really,” Ferguson said. “After that they withdrew Messi into central midfield and that made it very difficult for us. So concentration is going to be important in terms of attacking and defending. That will be the key for us.”