AS Monaco 1-2 Atletico Madrid
Atletico Madrid made a winning start their Group A campaign after defeating AS Monaco 2-1 at the Stade Louis II.
Samuel Grandsir put the hosts ahead after 18 minutes, before Diego Costa restored parity just after the half hour mark.
The winning goal arrived on the stroke of halftime, with Jose Jimenez heading home from Koke's corner.
Club Brugge 0-1 Borussia Dortmund
Christian Pulisic's 85th minute strike was enough to hand Borussia Dortmund a 1-0 win over Club Brugge.
Crvena Zvezda 0-0 Napoli
Napoli failed to secure maximum points in their opening game after they were held to a goalless draw at Stadion Rajko Mitić.
Galatasaray 3-0 Lokomotiv Moscow
Galatasaray showed their credentials in the opening group game after goals from Garry Rodrigues, Eren Derdiyok and Selcuk İnan secured a 3-0 win over Lokomotiv Moscow.
Schalke 1-1 FC Porto
Otavinho's penalty cancelled out Bree Embolo's 64th minute opener as Schalke and Porto sahred the spoils in Germany.
Porto's Alex Telles also had a penalty saved in the 13th minute.