An error by veteran goalkeeper Gianluigi Buffon saw Juventus held by Sassuolo at Allianz Stadium.Leonardo Bonucci opened the scoring after 20 minutes with a deflected strike before Jeremie Boga's deft chip levelled the scores shortly after.The away side then took the lead just after the interval as Buffon fumbled Francesco Caputo's effort into the net.Cristiano Ronaldo was on hand to equalise and save his team's blushes with a penalty with 22 minutes left.The hosts started well in Turin, as they attempted to make it five straight league wins, but Emre Can was unable to convert from close range in the opening moments.Maurizio Sarri's side then took a deserved lead when captain Bonucci's shot from the edge of the box was deflected into the far corner.But their lead only lasted two minutes as Boga beat the offside trap and lifted the ball over Buffon to make it 1-1.Sassuolo, who rise to 12th with this point, regularly tested Juventus' 41-year-old goalkeeper, and he was at fault when they eventually took the lead through Caputo.The veteran stopper was making his 645th Serie A outing but only his fifth of the season, meaning he is only two appearances from reaching Paulo Maldini's record of 647 games.Buffon's opposite number, Stefano Turati, who was making his senior debut for Sassuolo, impressed as he made several fine saves to keep out a Ronaldo free-kick, Gonzalo Higuain and Aaron Ramsey late on.But the young keeper, who was born 11 days after Buffon made his Serie A debut in August 2001, was unable to keep out Ronaldo's powerful spot-kick which earned the Serie A leaders a point.Ronaldo also had a goal ruled out for offside at 1-2.