Pep Guardiola will want to forget his return to the Camp Nou last night.
Barcelona thrashed Man City 4-0 last night to take control of Group C in the Champions League.
Guardiola had set-out his side to contain the Catalan side, but a brilliant hat-trick from Lionel Messi helped Barca to a crushing win against their former manager.
In the same group Celtic went down 2-nil at home to Borussia Monchengladbach at Parkhead.
Celtic manager Brendan Rodgers has admitted his side deserved to lose.
But in contrast, Arsenal produced a spectacular performance as they hammered Ludogorets Razgrad at the Emirates.
Mesut Ozil scored a second-half hat-trick for the Gunners after goals from Alexi Sanchez, Theo Walcott and Alex Oxlade-Chamberlain had already put Arsene Wenger's side in control.
