Juventus got back to winning ways after falling to their first league defeat of the season to Genoa before the international break.
Second-placed Napoli travel to Roma on Sunday looking to close the gap to 15 points with nine games remaining.
Ronaldo had been rested by Juventus against Genoa and the Portuguese star is now recovering from a right thigh injury picked up on international duty.
Argentina striker Paulo Dybala also pulled up with a thigh problem during the warm-up before Saturday’s game.
But coach Massimiliano Allegri insisted he had wanted to ease the pressure on Kean by opting for Rodrigo Bentancur to replace the Argentine.
“Scoring two goals for Italy in as many games, having all that attention, it uses up a lot of energy both physically and mentally,” said Allegri. “He (Kean) returned from international duty and looked like he barely knew where he was.
“He’s got the qualities to be a great player, but so did many who have lost their way over the years.”
Kean’s form, with goals for Italy against Finland and Liechtenstein, gives Allegri more options ahead of his side’s Champions League quarter-final against Ajax.
The youngster became the second youngest player after Mario Balotelli, aged 18 years and 242 days in 2009, to score eight Serie A goals.
“I’m ready to pursue new records,” he warned.
“What the Mister (Allegri) says is right: I hope to become like the greatest players in the world, through commitment and hard work.”
Juventus are without wingers Douglas Costa and Juan Cuadrado, with centre-back Andrea Barzagli also out injured.
The seven-time defending champions struggled to break down the Tuscans who were targeting a second straight win under new coach Aurelio Andreazzoli.
Empoli dug deep, allowing the hosts few opportunities, with Polish goalkeeper Bartlomiej Dragowski denying a Mandzukic header to the frustration of the home crowd.
Kean replaced Blaise Matuidi in the 68th minute and had an immediate impact, latching onto Mandzukic’s knock-down.
Ten minutes later, the teenager was denied a second, with a desperate one-handed save by Dragowski giving Empoli hope.
The Tuscany side remain one point above the relegation zone.
“It’s never easy after the break for international duty and it was good that we won like this, 1-0 with a struggle to get the points,” said Allegri.
“It’s another step forward.
“Now we have seven games in 20 days and fortunately we are recovering some players who can give us a big help.”
Earlier on Saturday, Igor Tudor got off to a winning start on his return as Udinese coach with a 2-0 victory over Genoa.
Former Croatian international Tudor took over a year after coming in and saving the north-eastern outfit from relegation with two wins in the last four games of the 2017-2018 season.
Stefano Okaka opening the scoring after just four minutes in Udine, finishing from a Seko Fofana cross.
Rolando Mandragora sealed a valuable three points with a volley just after the hour mark as Udinese gained some breathing space by moving four points above the relegation zone.
AC Milan, meanwhile, travel to Sampdoria later Saturday targeting third place ahead of arch rivals Inter, who moved ahead after winning their derby clash before the international break.