Simone Inzaghi’s team suffered their fourth defeat in their previous five league games as Monza shocked Inter Milan 1-0 on Saturday thanks to a late goal by defender Luca Caldirola.
After defeating Benfica 2-0 in the first leg of their quarterfinal match on Tuesday, Inter is on track to advance to the last four of the Champions League for the first time since 2010. Inter needed three points to go back into the top four.
They are now tied for fifth position with 51 points after 30 games, two points behind fourth-placed AC Milan after Bologna held them to a 1-1 draw earlier on Saturday.
For Inter, who had suffered three straight league defeats to Spezia, Juventus, and Fiorentina and drew 1-1 at Salernitana last weekend, it was their third home loss in a row—something that hadn’t happened in ten years.
Joaquin Correa, a striker for Inter, might have given his team a 1-0 lead in the 24th minute but Michele Di Gregorio, the alert goalkeeper for Monza, expertly saved the attempt.
Romelu Lukaku’s header was saved by Di Gregorio just before the hour after Inter progressively pressed for a goal after a first half devoid of obvious opportunities and quality.
A minute later, the Belgian striker had one more opportunity, but his curled effort from the outside of the area missed.
Forward Dany Mota almost scored for Monza in the 64th minute with a very similar shot.
As Caldirola met a corner and headed home from close range at the San Siro, the visitors unexpectedly seized the lead. The ball bounced off the ground and into the top left corner.
Substitute Inter’s finest chance to score an equalizer came from Lautaro Martinez, but two of his closest efforts were stopped by the goalie and one of them just missed the left post by an inch.
Dramatic Monza, who held Inter to a 2-2 draw in the rematch in January, rose one spot to 38 points and 12th position.
In their meeting on Saturday, Napoli and Hellas Verona were held to a scoreless draw.
On April 23, when Inter visit Empoli, who are in 14th position, they will play host to Fiorentina.