Defender Danilo opened the scoring for Juventus in the sixth minute when a corner found him unmarked on the edge of the box, and he drilled a powerful shot through a cluster of bodies into the net.
Gonzalo Higuain made it two six minutes later, latching on to a superb ball from Miralem Pjanic, but a shot into the top corner by Filip Djuricic in the 29th minute signalled the start of a spirited fightback by the home side.
They levelled six minutes into the second half when Domenico Berardi curled a beautiful free kick in at the near post, and Sassuolo went ahead three minutes later as Francesco Caputo stole in at the far post to steer in a wayward Berardi shot.
Ronaldo's best effort was an attempted lob in the first half that landed just wide, but he was well-shackled by the Sassuolo defence.
Instead it fell to left back Alex Sandro to produce a rare goal, meeting a 64th-minute corner with bullet header to level the scores.
Chasing their ninth league title in a row, Juventus poured the pressure on but could not force a winner.
"We struggle to maintain physical and mental continuity. It is difficult to understand why we have very good moments and others of passivity," Sarri said.
"It is difficult to understand, even allowing for the fact that we are meeting teams who are in extraordinary form. We have the feeling of ups and downs during the game," he added.