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.