The pair are two of the most valuable players in the world and have accounted for nine of PSG's 14 goals over the past four matches in all competitions.
There have been suggestions that France international Mbappe, 20, has occasionally felt frustrated with perceived favouritism towards Neymar, but the Brazilian insists there is no hidden animosity in their friendship.
"My relationship with Kylian is very good," Neymar told France Football.
"We are good friends and help each other to win matches, to score goals. I feel that there is something special. There is no competition between us.
"We help each other to score goals. When one of us scores, he tells the other one: 'now is your time.'
"This is the way to be in football – be a good team-mate, otherwise things won't go well."
PSG's next game is away to Le Mans in the Coupe de la Ligue on Wednesday.
Tuchel's side were paired with his old employers, Borussia Dortmund, when the draw for the Champions League last 16 was made on Monday.