MILAN: Lautaro Martinez's first-half brace put Inter Milan top of Serie A on Sunday with a 2-1 win over SPAL after champions Juventus were held 2-2 at home by Sassuolo.
"We didn't use our heads," lamented Juventus boss Maurizio Sarri after his side lost their first points at home this season.
Cristiano Ronaldo scored from the spot to rescue a point but Juventus slipped one point behind Antonio Conte's Inter Milan.
Argentinian Martinez put Inter ahead after 16 minutes at the San Siro, and then connected with Antonio Candreva's cross before the break to head in his eighth league goal this season.
Mattia Valoti pulled a goal back, but second-from-bottom SPAL fell to their ninth defeat.
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 held until their 2-1 defeat to 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 Juventus coach Conte.
"Now let's try to guard it jealously and enjoy it in the right way."
In Turin, Leonardo Bonucci struck early for the eight-time reigning Serie A champions but Jeremie Boga and Francesco Caputo hit back for Sassuolo before Ronaldo's point-saving intervention.
Sassuolo, in 12th, claimed their first ever point at Juventus, and held Sarri's unbeaten champions to their third draw of the 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.
"Every time we lost the ball we left ourselves open. We had a first half without application and little energy from the character point of view.
"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."
Ronaldo started up front, having missed last weekend's league game with a slight knee problem, as Paulo Dybala, who scored in their Champions League win over Atletico Madrid, started on the bench.
Eighteen-year-old Stefano Turati made an impressive debut in the Sassuolo goal, and pulled off a string of fine saves, denying Ronaldo, Gonzalo Higuain and Dybala late.
But Juventus counterpart Gianluigi Buffon had a nightmare. The 41-year-old, making just his fifth start this season, was at fault in Caputo's goal just after the break.
Bonucci got Juventus off the mark with a long-range effort on 20 minutes.
Three minutes later Boga pounced on a Caputo cross and sent it past an out-rushing Buffon from an angle.