Both Mbappe and Neymar scored one and set up two other goals as the French champions, who had already made sure they would end the group phase on top, finished with 16 points, five ahead of Real Madrid after the 13-time champions beat Club Brugge 3-1 away.
"Everybody has had something to say about us, but we have still won and topped our group with 16 points," PSG manager Thomas Tuchel told RMC Sport afterward. "That is not possible playing as individuals. We only conceded two goals across six matches. We are a team and the lads showed that here. I am convinced we will see that more and more."
Neymar played Mbappe through and the France international flicked the ball into the path of Icardi who poked home the ball to put the hosts ahead with his fifth Champions League goal this season -- his 12th in his last 13 games in all competitions.
Sarabia made it 2-0 three minutes later with an angled shot after being set up by Neymar. The Brazilian found the back of the net himself two minutes into the second half with a left-footed strike into the far corner after being set up by a Mbappe backheel.
"I am very happy after this game, as well as our style of play. Sometimes, we need to rest and are in stroll mode in Ligue 1," Neymar said. "The Champions League is also our ultimate aim. Everybody did well here and we are very satisfied by the way we played."
Mbappe, who has now scored 19 goals and set up 11 in 30 Champions League games, increased the advantage in the 63rd with a cool finish from another Neymar assist.
Fan favourite Cavani, who came on as a second-half substitute, rounded it off with a penalty in the 84th minute after Ryan Donk had brought down Mbappe.
"Edinson is an excellent penalty taker, a great player. All he was missing was a goal. He has scored and everybody can go home happy," added Neymar, who gave the ball to Cavani to get the goal.
PSG and Galatasaray fans clashed briefly before kickoff outside the stadium with one supporter being taken to hospital with a minor injury, a police source said.