Harry Kane netted a stoppage-time winner from the halfway line at the National Stadium after goals from Erik Lamela, Gonzalo Higuain, Ronaldo and Lucas Moura:
It was Sarri's first game in charge since he was appointed Massimiliano Allegri's successor last month.
"Cristiano's the best player in this team. Therefore, we must set up the other 10 well defensively. He can play anywhere on the field. He's the best, and it's important for him to be free on the pitch. The positive aspect with Higuain is his attitude. Gonzalo's looking good in training."
Matthijs de Ligt made his debut for Juve against Spurs following his €75 million (£67.8 million) move from Ajax earlier this week.
Other key additions to the Old Lady squad this summer have included Aaron Ramsey and Adrien Rabiot, both signed on free transfers from Arsenal and Paris Saint-Germain, respectively.
Sarri hinted, though, that the Italian champions are not yet done with their business, per Football Italia:
"I think the club, between now and the end of the transfer window, will do something in terms of incomings, but we'll also have to do something in terms of outgoings."
Juventus have won the last eight Serie A titles in succession, so Sarri's key aim for next season will be to guide his new club to UEFA Champions League glory.
The 60-year-old only earned his first piece of major silverware last term when he won the UEFA Europa League with Chelsea.
Juve were runners-up in Europe's elite competition in 2014-15 and 2016-17, but they have fallen at the quarter-final stage in both the last two campaigns.