Match ends, Inter Milan 0, Parma 1.
Inter Milan's poor start to the season continued as Federico Dimarco scored a brilliant winner for Parma against his parent club at the San Siro.
The 20-year-old, on loan from Inter, won the ball in midfield and smashed a 25-yard strike into the top corner.
The goal was the full-back's first in Serie A and gives Parma their first win since returning to the top flight.
Inter, who play Tottenham in the Champions League on Tuesday, have only won one of four matches this season.
Dimarco came through the youth teams at Inter before he was loaned to Ascoli and Empoli and sold to Swiss club Sion.
Inter re-signed the left-back in July but loaned him to Parma the following month.
He also prevented his parent club taking the lead just before the hour when he cleared Ivan Perisic's effort off the line.
Inter, tipped as one of the favourites for the Serie A title, have just four points from four matches this season.
Parma have won three consecutive promotions back into the top flight after going bankrupt in 2015.
Match ends, Inter Milan 0, Parma 1.
Second Half ends, Inter Milan 0, Parma 1.
Foul by Marcelo Brozovic (Inter Milan).
Antonino Barillà (Parma) wins a free kick in the defensive half.
Attempt missed. Ivan Perisic (Inter Milan) left footed shot from outside the box misses to the right.
Attempt blocked. Stefan de Vrij (Inter Milan) right footed shot from the centre of the box is blocked. Assisted by Matteo Politano.
Attempt missed. Radja Nainggolan (Inter Milan) right footed shot from outside the box misses to the left. Assisted by Ivan Perisic.
Attempt blocked. Ivan Perisic (Inter Milan) right footed shot from outside the box is blocked. Assisted by Matteo Politano.
Attempt saved. Roberto Inglese (Parma) right footed shot from the centre of the box is saved in the top centre of the goal.
Attempt saved. Gervinho (Parma) right footed shot from the centre of the box is saved in the centre of the goal. Assisted by Luigi Sepe.
Corner, Inter Milan. Conceded by Riccardo Gagliolo.
Offside, Parma. Antonino Barillà tries a through ball, but Roberto Inglese is caught offside.
Attempt missed. Roberto Gagliardini (Inter Milan) header from the centre of the box is too high. Assisted by Matteo Politano with a cross following a corner.
Corner, Inter Milan. Conceded by Riccardo Gagliolo.
Attempt blocked. Matteo Politano (Inter Milan) left footed shot from outside the box is blocked. Assisted by Radja Nainggolan.
Attempt missed. Roberto Inglese (Parma) right footed shot from outside the box is too high.
Offside, Parma. Bruno Alves tries a through ball, but Gervinho is caught offside.
Foul by Kwadwo Asamoah (Inter Milan).
Roberto Inglese (Parma) wins a free kick in the attacking half.
Federico Dimarco (Parma) is shown the yellow card for excessive celebration.
Goal! Inter Milan 0, Parma 1. Federico Dimarco (Parma) left footed shot from outside the box to the top right corner.
Attempt blocked. Gervinho (Parma) right footed shot from the left side of the box is blocked. Assisted by Leo Stulac.
Corner, Inter Milan. Conceded by Francisco Sierralta.
Substitution, Parma. Francisco Sierralta replaces Simone Iacoponi.
Foul by Milan Skriniar (Inter Milan).
Roberto Inglese (Parma) wins a free kick in the defensive half.
Attempt missed. Antonino Barillà (Parma) left footed shot from outside the box is high and wide to the left. Assisted by Leo Stulac.
Corner, Inter Milan. Conceded by Riccardo Gagliolo.
Attempt missed. Ivan Perisic (Inter Milan) header from the centre of the box misses to the right. Assisted by Matteo Politano following a corner.
Corner, Inter Milan. Conceded by Simone Iacoponi.
Attempt saved. Radja Nainggolan (Inter Milan) right footed shot from outside the box is saved in the centre of the goal. Assisted by Kwadwo Asamoah.
Substitution, Inter Milan. Kwadwo Asamoah replaces Danilo D'Ambrosio because of an injury.
Offside, Inter Milan. Radja Nainggolan tries a through ball, but Mauro Icardi is caught offside.
Attempt blocked. Roberto Inglese (Parma) right footed shot from outside the box is blocked. Assisted by Alessandro Deiola.
Danilo D'Ambrosio (Inter Milan) is shown the yellow card for a bad foul.
Foul by Danilo D'Ambrosio (Inter Milan).
Riccardo Gagliolo (Parma) wins a free kick in the defensive half.
Delay over. They are ready to continue.
Substitution, Parma. Alessandro Deiola replaces Antonio Di Gaudio.
Delay in match Luigi Sepe (Parma) because of an injury.