Juventus Angel Di Maria goes for the ball during the Serie A soccer match between Monza and Juventus, in Monza, Italy, Sunday, Sept. 18, 2022. AP
Promoted Monza probably didn't expect its first-ever Serie A win to come against Juventus but it managed to beat Massimiliano Allegri's side 1-0. Juventus played most of the match with 10 men following Angel Di Maria's red card.
Simone Inzaghi's Inter side was earlier beaten 3-1 at Udinese, for its third loss of the season.
AC Milan played Napoli later Sunday. The two sides headed into the weekend level at the top of the table with Atalanta, which was playing at Roma.
Allegri was already under pressure after Juventus lost its second straight Champions League match midweek. It was unbeaten in Serie A but had only won two of its opening six matches.
The Bianconeri were perhaps expecting an easier match at Monza, which was winless and had conceded 14 goals in its six games.
However, Juventus had barely a sight of goal and its chances of getting a morale-boosting win diminished when Di Maria was needlessly sent off in the 40th minute for elbowing Monza defender Armando Izzo forcefully in the chest.
And the home fans went wild in the 74th when Patrick Ciurria whipped in a cross from the right and Christian Lund Gytkjær volleyed in at the near post.
Monza is owned by former AC Milan owner Silvio Berlusconi.
Udinese continued its surprising start to the season and moved top of the table - for a few hours at least - with its fifth straight win.
Nicolo Barella curled in a fantastic free kick in the fifth minute to get Inter off to the perfect start but Udinese leveled in the 22nd when Roberto Pereyra's free kick went in off Milan Skriniar for an own-goal.
Udinese hit the post before Jaka Bijol headed in a corner with three minutes remaining and Tolgay Arslan made sure of the points in stoppage time with a diving header.
Also, Lazio won 4-0 at Cremonese and Fiorentina beat Hellas Verona 2-0.