Barcelona scored twice in eight minutes as they came from behind to beat Borussia Monchengladbach 2-1 in their Group C tie in Germany.
Thorgen Hazard's 34th-minute opener put the Bundesliga side on top but Arda Turan equalised before Gerard Pique scrambled home the winner after home goalkeeper Yann Sommer failed to hold Luis Suarez's shot.
Barca are now top of Group C after Celtic held Man City to a 3-3 draw in Glasgow
Paris St Germain joined Arsenal on four points in Group A after coming from behind to win 3-1 in Bulgaria.
Ludogorets took a 15th-minute the lead through Natanael but PSG earned the points thanks to Blaise Matuidi's equaliser and an Edinson Cavani double.
Arsenal ran out comfortable 2-0 winners over Basel in London.
Last year's runners-up Atletico Madrid recorded an impressive 1-0 win at home to Bayern Munich, the team they beat in last season's semi-finals.
Belgium international Yannick Carrasco's first-half strike earned Diego Simeone's side victory despite Atletico striker Antoine Griezmann missing a late penalty.
Bayern remain second in Group D after the other game between Rostov and PSV ended in a 2-2 draw.
Rostov led twice through goals from Dmitry Poloz but Davy Propper and Luuk de Jong equalised on each occasion before Propper missed the chance to win it from the penalty spot.
In Group B, Dries Mertens scored twice as Napoli romped to a 4-2 win against Benfica while Besiktas and Dynamo Kiev drew 1-1 in Turkey.
