Inter Milan failed to take advantage of Juventus' defeat to AC Milan on Sunday as they fell to a 1-0 defeat at Parma.
Nicola Sansone scored the only goal of the game 15 minutes from time to give Parma a deserved win at the Stadio Ennio Tardini.
Inter were once again off colour, losing for the second time in three games since beating Juve 3-1 in Turin.
It was an indication of what was to come when Walter Samuel almost turned a cross into his own goal in the fourth minute, but Samir Handanovic was alert to the danger.
Parma certainly had no fear and continued to attack their opponents, whose only shot in the first half came from Esteban Cambiasso, but the ball was blocked on the line.
Jonathan Biabiany was particularly inspired against his former club and his shot in the 44th minute flew just wide of the far post with Handanovic standing idly by, unable to intervene even had the shot been on target.
Five minutes into the second half, Biabiany flicked a header just wide of the far post as Parma continued to dictate affairs.
A free-kick from Jaime Valdes was deflected off the knee of Cambiasso, but Handanovic had the shot covered.
Parma gained a deserved lead in the 75th minute when Sansone picked up possession inside his own half and set off on a 30-yard run which culminated in a low shot into the bottom left-hand corner of Handanovic's goal.
Inter had 15 minutes left to muster an equaliser, but it was Parma who seemed more likely to score with Yohan Benalouane's header tipped over the crossbar five minutes from time.
Parma easily held on to the win which lifted them to seventh in the table and above AC Milan, maintaining an unbeaten home record that stretches back to March.