Juve came from behind to win 2-1 at newly promoted Brescia as it climbed above rival Inter, which has a game in hand, at the summit.
Alfredo Donnarumma had given Brescia an early lead before a Jhon Chancellor own goal and superb strike from Miralem Pjanic transformed the contest on what was Mario Balotelli's debut for Juve's opponent.
Juve achieved the result without superstar Cristiano Ronaldo, who was left out as a precautionary measure with an adductor problem.
While there were plenty of positives for Sarri to take, the former Chelsea head coach conceded there remains work to be done, particularly in a defence which has now conceded five times in its opening five league matches.
"We improved our passing with the 4-3-1-2 formation played," Sarri said. "I saw some steps forward in the chances created.
"We need to improve the defence. Which formation will we use? We can use both solutions. We struggle with offensive wingers at this time while we have a lot of quality midfielders so it seemed obvious to try this formation.
"Then, if a month from now the wingers find their form, we can evaluate the options, but the team must be prepared with both formations."
Asked about the performances of defender Matthijs de Ligt, a €75million close-season arrival, Sarri added: "He's improving a lot, he needs time."
Sarri was impressed with the performance of out-of-favour attacker Paulo Dybala, who played a part in both goals for his team
"Dybala had a good match both offensively and defensively," Sarri said. "He was excellent with quick passes and he left the pitch hurting. We hope he can recuperate for the next game [SPAL on Saturday]."