Juventus, chasing an eighth successive title, have six points from two games after a somewhat fortunate win, but Ronaldo is still waiting for his first goal since his move from Real Madrid.
Piotr Zielinski scored twice as Napoli came from two goals behind to beat AC Milan 3-2 and give new coach Carlo Ancelotti an unforgettable home debut, especially as it came against the side where he spent eight seasons of his coaching career.
Striker Gonzalo Higuain also made his debut for AC Milan following his loan move from Juventus, but he had little impact.
Miralem Pjanic rifled Juventus ahead in the 30th minute with a shot from outside the area before the Turin side added a second in the 75th minute in untidy fashion.
Joao Cancelo's low cross from the right was partially intercepted by Lazio goalkeeper Thomas Strakosha but he succeeded only in pushing the ball to Ronaldo.
The Portuguese turned the ball towards goal with his right foot but his left heel blocked the shot and the ball rebounded into the path of Croatia World Cup forward Mandzukic, who swept it home.
The closest Ronaldo came to breaking his duck was with a vicious dipping effort on the turn in the 71st minute, but it was brilliantly turned over the bar by the Albanian goalkeeper.
Juventus goalkeeper Wojciech Szczesny, again preferred ahead of new signing Mattia Perin, made two key saves in the first half, turning Senad Lulic's shot around the post and then charging out of his goal to block a dangerous Marco Parolo break.
"Italian football is completely different to Spain. Ronaldo understands that and he is settling in very well," said Juventus coach Massimiliano Allegri.
"There was a risk of us getting carried away by the enthusiasm created by Ronaldo's first home appearance," added the coach, who picked Blaise Matuidi and Federico Bernardeschi ahead of Paulo Dybala and Juan Cuadrado.
"I have a very strong squad and have to evaluate everyone. We needed these characteristics in midfield today," he said. "There are times we are too frenetic and other moments when we go to sleep. We have to find a better balance."
AC Milan stunned the San Paolo when Giacomo Bonaventura's unorthodox volley put them ahead in the 15th minute and Davide Calabria drove in the second from Suso's clever layoff four minutes after halftime.
Zielinski pulled one back three minutes later, rolling the ball into the far corner from the edge of the area after Milan lost possession in their own half, and from then on a Napoli fightback looked to be on the cards.
The Pole drove home the equaliser in the 67th minute after an attempted Milan clearance from a corner landed at his feet and substitute Dries Mertens completed the job with 10 minutes left, turning in Allan's low cross at the far post.
There was another big cheer shortly afterwards when Higuain shot high and wide from his only real opening of the match.
The win left Napoli, last season's runners-up under Maurizio Sarri, with six points from their first two games.
(Writing by Brian Homewood, editing by Pritha Sarkar, Neville Dalton)
Share
