Shamrock Rovers hosted their first match at this level by welcoming French giants PSG to the Tallaght Community Stadium, and held out for five and a half minutes before Thiago put the visitors in front. Ander Herrera and Marek Hamsik scored either side of the break to seal a 3-0 away win.
Barcelona and Juventus picked-up big away wins in Group H, and will likely have a second win apiece before they clash in Turin in five weeks. The holders were held to a 1-1 draw at home by Valencia, with the other Group G match also finishing 1-1 between Legia Warsaw and Standard Liège.
Elsewhere, Twente went in front three times against Arsenal but were pegged-back each time, while Olympiakos beat Young Boys in Greece., and Sporting Lisbon and Manchester United held each other to a goalless draw.
Teams are back in action in a fortnight.
UEFA CHAMPIONS LEAGUE: WED 17 SEPTEMBER E FC Twente 3-3 Arsenal E Olympiakos 2-1 Young Boys F Shamrock Rovers 0-3 Paris Saint-Germain F Sporting Clube de Portugal 0-0 Manchester United G Borussia Dortmund 1-1 Valencia G Legia Warsaw 1-1 Standard Liege H AS Monaco 2-4 Barcelona H Rubin Kazan 1-4 Juventus UEFA CHAMPIONS LEAGUE: TUE 16 SEPTEMBER A Anderlecht 1-2 Olympique Lyonnais A Chelsea 2-0 Rapid Vienna B Dinamo Zagreb 1-3 Fenerbahçe B Zenit St Petersburg 2-0 Bayern Munich C Benfica 2-0 Metalist Kharkiv C Real Madrid 2-1 FSV Mainz D Tottenham Hotspur 2-3 Celtic D Villarreal 0-3 AC Milan