The 41-year-old Buffon is closing in on Paolo Maldini’s record for Serie A appearances in what is likely to be his final season.
Rivals Inter Milan took full advantage of Juventus’ slip, taking pole position with a 2-1 win over SPAL as the champions slipped to second, one point behind, after dropping their first points at home this season.
Buffon started in place of Polish goalkeeper Wojciech Szczesny.
It was Buffon’s 645th Serie A appearance but only his fifth of the season, putting him two short of Maldini’s record of 647 games.
However, it was not a memorable afternoon with Jeremie Boga pulling Sassuolo level at 1-1 after chipping the ball over an onrushing Buffon.
The goalkeeper then fumbled in Francesco Caputo’s goal for 2-1 after a mix-up in the Juventus defence after the break before Cristiano Ronaldo rescued a point with a 68th-minute penalty.
Sarri said the team shared the blame and not just Buffon.
“Gigi? We focus on his ‘blunder’, but everything starts in the build-up, the chain of errors is quite obvious,” said the former Chelsea and Napoli boss.
“It was an incredible series of mistakes, from a bad back-pass to another that hit a Sassuolo player.
“When you aren’t fully focused, a blunder can happen. As I said, we didn’t use our heads, certain episodes are explained like this.
“Up front we had 27 shots and two goals… behind we had three slip-ups in the same action, which lead to Sassuolo going 2-1.
“No one is immune from responsibility. Cristiano Ronaldo? I saw him more alive in the 30 final minutes than in the initial phase.”
Buffon returned to Juventus this season after a season with Paris Saint-Germain as he pushes to close in on the record for Serie A appearances.
His contract with Juventus is reported to include a special clause, whereby Sarri will have to play him in at least eight league games.
This is the number that he needs to overcome Maldini’s record.
Buffon was capped 176 times by his country and won the 2006 World Cup.
He also won nine Serie A titles and four Italian Cups with Juve after signing from Parma in 2001.
As the veteran struggled, 18-year-old Stefano Turati made an impressive debut in the Sassuolo goal, denying Ronaldo, Gonzalo Higuain, Paulo Dybala and Aaron Ramsey late on.
“It was an incredible emotion,” said Turati. “The most difficult save? That on Ronaldo,” he said of a free-kick he kept out from the Portuguese star.
“Buffon told me ‘very good’, it was an honour to play against him, the idol of all the children. I too, when I was a boy, watched him.”
Buffon joined Juventus in 2001, the year that Turati was born.
