Mbappe, 18, was guilty of wasting four clear-cut chances before deflecting in a late consolation for reigning champions Monaco, who lost 2-1 to runaway Ligue 1 leaders PSG on Sunday.
It was Mbappe's first time back at the Stade Louis II since leaving for PSG on an initial loan deal, having scored 26 goals in all competitions to guide Monaco to Ligue 1 glory and the Champions League semi-finals last term.
Afterwards, Silva jokingly told reporters: "I told him in the locker room that he still thought he was playing for Monaco.
"He even deflected the ball on their goal!
"But Kylian has a very good start to the season, like Cavani and Neymar."
Mbappe misses another great chance for PSG... and is booed by the Monaco fans! 👎 pic.twitter.com/x55zOac9Ls— Goal (@goal) November 26, 2017
Edinson Cavani and Neymar scored for PSG, who moved nine points clear of Monaco in France's top flight.
Cavani broke the deadlock away from home before Neymar doubled PSG's advantage courtesy of a 52nd-minute penalty.
Neymar converted the spot-kick, having been handed penalty duties by head coach Unai Emery following his on-field spat with Cavani on September 18.
Asked about Neymar taking penalties, fellow Brazilian Silva said: "What we saw today, Neymar shooting a penalty... perhaps in a next match, Neymar can leave it to Cavani because this kid has a great heart, you don't even imagine it.
"Perhaps, if he had already scored today, he could have let the penalty to Cavani because the most important thing is that PSG can win and Neymar makes this kind of thing. Maybe for the next penalty, he can pass it even to Kylian because today he had some difficulty in scoring, but we are happy with him."