Ronaldo turned the ball into the net from two metres to give Juventus a 1-0 lead in the 50th minute after a Sassuolo defender headed the ball against his own post and the rebound left the Portugal forward with an empty net.
Cristiano Ronaldo has ended a 320-minute wait for his first Juventus goal by netting against Sassuolo.
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Five minutes into the second half, the hosts broke the deadlock as Ronaldo finally opened his account with simple finish from point-blank range.
The former Bayern Munich winger was not blown up for a strong challenge on Federico Di Francesco in the build-up to the visitor's goal and appeared to elbow him as he attempted to get back to his feet.
Juventus, seeking a record-extending eighth successive Serie A title, are the only team still with a ideal record.
The Brazilian was given his marching orders after VAR caught him spitting in the face of Sassuolo midfielder Federico Di Francesco in the 93rd minute with the two having clashed throughout Sunday's Serie A clash at the Allianz Stadium.