My perception was the Barça did not look to well tuned, especially the first half. But FC Barcelona is currently the "Best Club in The World" & their star players managed to pull the stones out of the fire to seal the result.
A hard worked endeavour as Leverkusen had some excellent chances & opportunities at goal that if converted would have radically changed the final score-line. They scored their only goal via a KADLEC header in the 52nd min & later had some "bad luck" hitting Barça goalie Valdes & the post.
The difference was ALEXIS with two vital goals ( 41st & 55th min) & MESSI with the third in the 88th min. These guys don´t miss many opportunities & they took them with important away goals. Even at "half gas" they manage to pull things through.