Ronaldo himself twice came close to scoring, forcing a superb save from Lazio keeper Thomas Strakosha and then seeing a cross come off his heel in the six-yard box – though the rebound fell to Mandzukic to score.
The result means Juventus, who have won the last seven Serie A titles, stay top of the table after two games, ahead of Napoli on goal difference, with last season’s top two the only sides to have won both their opening games.
Lazio, on the other hand, have lost their first two and are bottom of the table, with last season’s fifth-placed finishers having had the misfortune of facing Napoli and Juventus to start the season.
The Bosnia and Herzegovina midfielder has spent the past two seasons with the Bianconeri and has agreed to stay until the end of the 2022/23 campaign.
Pjanic, 28, has helped Juve won the Serie A and Coppa Italia double in both of his seasons at the club following five productive but trophy-less years at Roma.
A statement on the club website read: “Juventus are delighted to announce that Miralem Pjanic has renewed his contract at the club until 2023.
“Since arriving prior to the 2016/17 season, Pjanic has become an increasingly-integral part of the Bianconeri midfield, providing pin-point passes across the pitch while firing free-kicks into the back of the net with outstanding consistency.”
Juventus coach Massimiliano Allegri accepts it will take time for Cristiano Ronaldo to fully settle in after his side battled to a dramatic 3-2 victory at Chievo, which shows how hard their serie a title defence will be.
Portugal forward and Ballon d’Or holder Ronaldo took centre stage at the Bentegodi on his competitive debut following a €100m summer transfer from Real Madrid.
However, it needed a huge team effort and a last-gasp winner from the defending champions to secure three points in Verona.
Following a minute’s silence in memory of the victims of Tuesday’s bridge collapse in Genoa, Sami Khedira gave Juve an early lead, which was cancelled out by a towering header from Mariusz Stepinski.
Chievo went 2-1 ahead from the penalty spot early in the second half through a penalty from former Juve winger Emanuele Giaccherini, only for an own goal by defender Mattia Bani to level things up again.
Substitute Mario Mandzukic thought he had won it with a late header, given by goal-line technology, only for the effort to be ruled out following a referral by the Video Assistant Referee after Chievo goalkeeper Stefano
Sorrentino had taken a heavy blow from Ronaldo in the build-up.
Juve, aiming to deliver a record eighth successive serie a crown, showed the spirit of champions to score a legitimate winner deep into five minutes of stoppage time when substitute Federico Bernardeschi turned in a low cross from Alex Sandro.
“It makes us realise how tough it’s going to be to win the league again,” Allegri said afterwards to the club website.
“We made a lot of mistakes today and let our focus drop. You think you’re in control and you ease off a touch, then you let your opponents get crosses in, you defend badly and you end up conceding.
“In any case, a game like that will only do us good because it makes us realise how tough it’s going to be to win the league again.”
Allegri accepts it will take time for his men to find their rhythm alongside a their new talisman.
“We’ve only had the whole squad training together for seven days,” he said.
“We’re still getting to know (Cristiano) Ronaldo. He linked up well with (Paulo) Dybala today and I was impressed by how easily he slotted into the team.
“It’s a shame he couldn’t score himself, but Sorrentino denied him a couple of times. He was happy we got the win anyway.
“(Joao) Cancelo played well in the first half, then he gave away the penalty and felt guilty about it – but you mustn’t get down over something like that.”