The Uruguayan striker rounded off the scoring late on with an audacious header, having earlier netted from the penalty spot in the first half.
Relive how the 90 minutes of action unfolded with Sports Mole's live text coverage below.
STARTING XI: Gordon; Ralston, Lustig, Simunovic, Tierney; Brown, Ntcham; Roberts, Armstrong, Sinclair; Griffiths
SUBS: De Vries, Bitton, Ajer, McGregor, Rogic, Edouard, Forrest
STARTING XI: Areola; Alves, Silva, Marquinhos, Kurzawa; Motta, Verratti, Rabiot; Neymar, Mbappe, Cavani
SUBS: Trapp, Meunier, Kimpembe, Yuri Berchiche, Lo Celso, Lucas, Draxler
Brendan Rodgers: "We just aim to play our game, based around being aggressive defensively and having a physical edge. If you stand off top-class players they will show you why they are top class. The quality they have been building over the last few years and what they have done over the summer - bringing in Neymar and [Kylian] Mbappe, who is an amazing young striker - their focus clearly is on winning it."
Unai Emery: "I know of [Griffiths's] quality, how well he plays on the ball and how well he keeps the ball. He has a lot of experience. We've analysed the style of the team and his style as well and we'll try and adapt for him. I'm obviously aware there is a great atmosphere here. All the players love to play this type of game. My players are used to playing at this level, in this type of atmosphere. It will be difficult for us to overcome but we aim to try and do that."
CELTIC SUBS: De Vries, Bitton, Ajer, McGregor, Rogic, Edouard, Forrest
PARIS SAINT-GERMAIN SUBS: Trapp, Meunier, Kimpembe, Yuri Berchiche, Lo Celso, Lucas, Draxler