As the final whistle blew Bruno Guimarães wore a mischievous smile, Enzo Le Fée was a study in dejection and Arsenal’s immaculate start to the season remained unblemished. Two minutes after David Raya had, rather majestically, saved Le Fée’s second half penalty, Guimarães delighted both his new north London public and plenty of old friends in Newcastle by sending a shot curving past Robin Roefs. Yet no one should be deceived by the emphasis lent to the scoreline by Bukayo Saka’s stoppage-time p…