There was a moment in the first half when the camera found Pep Guardiola, seated among the other awe-struck socios at Camp Nou, with his head in his hands. Lionel Messi had, in the midst of a performance of breathtaking virtuosity, spotted James Milner charging towards him by the touchline and reacted, in one minimalist motion, by poking the ball through the Englishman’s legs and nonchalantly jogging away as his opponent crumpled to the floor.