The 33-year-old went three games without scoring for the Turin-based side before the game but he was on hand to score an easy tap-in five minutes into the second half.
The visitors failed to clear a corner before the ball rebounded off the post with Ronaldo just needing to touch the ball to get off the mark for Juve.
Cristiano Ronaldo passionately celebrates after scoring his first goal for Juventus on Sunday
Sassuolo failed to clear a Juventus corner which led to Ronaldo easily finishing the chance
The 33-year-old is swamped by his team-mates following his opening goal for the club
The forward passionately celebrated with the home fans before showing off his signature celebration for the first time at the Allianz Stadium.
It was RonaldoXCHARXs 28th attempt on goal for Juventus while it was also his 400th league goal in his career.
With the weight lifted off his shoulders, Ronaldo was on the war path as Juventus went in search for the second goal.
And it only took 15 minutes for Ronaldo to get his brace.
He scored his second just 15 minutes after his first after he was slipped through by Emre Can
Ronaldo accurately drilled the ball low past Andrea Consigli (not pictured) in the second half
The Portuguese forward celebrates scoring his second goal for Juventus on Sunday
His second was more of a typical ‘Ronaldo goal’ – Juventus broke quickly which lead to a four attackers running at two defenders as the five-time Ballon d’Or winner sprinted ahead of Emre Can who carried the ball up the field.
The German midfielder slipped Ronaldo through before he powered a low-driven shot across the path of the keeper to give Juventus a huge advantage.
However, Sassuolo gave Juventus a late scare when Khouma Babacar scored in the 91st minute to make it 2-1 at the Allianz Stadium.
Ronaldo is congratulated by his Juve team-mates following his second goal for the club
Juventus saw out the result but were down to 10 men after substitute Douglas Costa saw red in the dying moments.
While he may have struggled to break his duck up until Sunday, Ronaldo was a constant threat in three previous fixtures for the Old Lady.
He came close to scoring in their 3-2 win over Chievo on the opening day of the season before he was denied again in both games against Lazio and Parma.