Supporters at Stamford Bridge had called for the talented 18-year-old to be brought on before his 78th-minute introduction and he justified the hype with an impressive cameo.
"He does not have to do anything to convince me", Chelsea's head coach insisted.
"I think to have pressure when you are 18 is very risky for a player", said the Italian.
"When you have pressure when you are 18 it is unsafe, you can lose the target". When you're 18 the target is to improve - to improve, tactically, mentally and physically.
"It's risky for him. This is why I don't like to speak about him".
"So for now we need him to improve without the pressure of the media, the fans, the club". I think that in England he is the only (player born in) 2000 with 16 matches in the first team.
In the January transfer window, Chelsea allowed Victor Moses to leave and join Fenerbahce, indicating that Zappacosta could yet play a part for the Blues.
The divisions in the fanbase, mainly between the online fans who tend pro-Sarri, and the match-going punters who, by and large, have never taken to him, have reached really poisonous levels at times this season.
Pulisic's signing also questions Sarri's theory on being a top player as it means they've spent £58 million on a player they don't expect to be a top player for another two or three years. He needs to improve because he can arrive at the top only at 22 or 23, like every other player.
The goal came from a fine Chelsea move, which saw quick passing and running all the way from the back before Hudson-Odoi finally calmly finished. "To not concede a goal at home is very important in this competition", said Sarri.