Lautaro Martinez's first-half brace sent Inter Milan top of Serie A on Sunday with a 2-1 win over SPAL after champions Juventus were held at home by Sassuolo, reports AFP.
"We didn't use our heads," lamented Juventus boss Maurizio Sarri after his side dropped their first points at home this season.
Cristiano Ronaldo scored from the spot to rescue a 2-2 draw but Juventus slipped one point behind Antonio Conte's Inter.
Argentinian Martinez put Inter ahead on 16 minutes at the San Siro, and then headed in Antonio Candreva's cross to score his eighth league goal this season.
Mattia Valoti pulled a goal back, but second-from-bottom SPAL fell to their ninth defeat of the campaign.
Conte has guided Chinese-owned Inter to 12 victories in 14 league games for the first time, and they reclaimed the top spot which they had previously held until their 2-1 defeat by Juventus on October 6.
"When a team like Juventus drops points, you need to make sure that you make the most of that," said former Juve coach Conte.
In Turin, Leonardo Bonucci struck early for the eight-time reigning champions but Ivorian Jeremie Boga and Francesco Caputo hit back for Sassuolo before Ronaldo's intervention. Sassuolo, in 12th, claimed their first ever point at Juventus, and held Sarri's unbeaten champions to their third draw this season.
"We got into trouble on our own, we didn't use our heads in the first half, as the goals conceded show," said Sarri.
"But we were coming off two games in which we used up a lot of energy against Atalanta and Atletico Madrid. We woke up after going behind."
Veteran Gianluigi Buffon endured a nightmare in the Juventus goal.
The 41-year-old was making just his fifth start this season, putting him two short of Paolo Maldini's record of 647 Serie A appearances.
Boga dinked the first Sassuolo goal on 22 minutes over the onrushing Buffon, who then fumbled in Caputo's second after the break following a mix-up between Juan Cuadrado and Matthijs de Ligt.