The 33-year-old Portugal forward, playing his fourth game for Juve, had two great chances to add to the brace, but shot off-target on each occasion.

Sassuolo pulled a goal back in stoppage time through Khouma Babacar before Juve's Douglas Costa sent off for spitting in the face of Federico Di Francesco after the intervention of the video assistant referee.

Ronaldo, who had played the full duration of each of Juve's previous three Serie A games, looked eager to register his first goal since his July move as Sunday's contest at the Allianz Stadium got underway.

In the sixth minute he saw a shot from the edge of the box deflect behind off Rogerio and in the 11th he beat the turf in frustration after connecting with Alex Sandro's cross but getting his header wrong, sending it wide.

Emre Can, making his full Juve debut after his move from Liverpool, then struck off-target before Gianmarco Ferrari's header was caught by Wojciech Szczesny at the other end.

Juventus were starting with Ronaldo, Paulo Dybala and Mario Mandzukic all together for the first time, and the latter pair both had shots blocked in the 25th minute after Marlon lost possession in the Sassuolo area. Ronaldo then hit a free-kick wide from around 35 yards out.

Towards the end of the first half Sassuolo's Pol Lirola almost scored an own goal, with Andrea Consigli doing well to keep the ball out, before Alfred Duncan fired into the Juve net, but the effort did not count as referee Daniele Chiffi's whistle had gone just beforehand for a Filip Djuricic foul on Joao Cancelo.

Ronaldo then opened his account with a simple prod in.

After the ball came into the box from a corner, it went via Leonardo Bonucci and a touch off Duncan to Ferrari, whose header came back off his own post, and Ronaldo was there to convert the follow-up.

Kevin-Prince Boateng backheeled wide as Sassuolo tried to hit back swiftly before Ronaldo bagged his second, collecting Can's pass and beating Consigli with a low shot.

As he looked to complete a hat-trick, Ronaldo brought a save out of Consigli in the 73rd minute and then had a penalty appeal waved away when he went down in the box having been challenged by Ferrari.

Szczesny produced a fine save to keep out a Duncan effort seconds later before Ronaldo twice passed up chances when appearing certain to score, shooting either side of the target.

Sassuolo substitute Babacar reduced the deficit in with a header before Costa, who had come on for Can, took the gloss off Juve's win.

The Brazilian had got in a tangle with Di Francesco in the build-up to the goal and appeared to try to headbutt him afterwards.

Chiffi gave him a yellow card at that point, but, after footage then showed Costa spitting in Di Francesco's face, VAR intervened to send him off.