Holders Barcelona barely paused for breath in a ruthless 5-0 hammering of BATE Borisov while former champions AC Milan took their time to get started before overcoming new boys Viktoria Plzen 2-0 in the Champions League early this morning. Lionel Messi scored twice in a dominant Barca performance on a rainy night in Minsk as the Spaniards went joint top of Group H, along with Milan after the Italians needed second-half goals to break the deadlock against Plzen. English sides Arsenal and Chelsea had mixed fortunes in nervy endings to their games as Arsene Wenger\'s side held on to an early lead to beat visitors Olympiakos Piraeus 2-1 while Chelsea conceded a late penalty to draw 1-1 in Valencia. Arsenal, whose eighth-minute opener came from teenager Alex Oxlade-Chamberlain on his European debut, have four points in Group F, sitting behind Olympique Marseille who maintained their perfect start with a 3-0 victory over Borussia Dortmund. Chelsea\'s Juan Mata had been on the verge of a winning return to his old stomping ground in Valencia after Frank Lampard\'s opener before substitute Salomon Kalou handled to give away an 87th-minute penalty that Roberto Soldado converted.