AC Milan slumped to a 2-0 loss against Sassuolo after being reduced to 10 men for over an hour, with Domenico Berardi and Armand Laurienté on target.
The Rossoneri entered the clash aiming to close the gap on second-placed Napoli and strengthen their grip on a Champions League spot.
However, they were without Luka Modric, whose season has ended following surgery on a fractured cheekbone. Ardon Jashari was drafted into the lineup, while Christopher Nkunku replaced the struggling Christian Pulisic.
Sassuolo welcomed back Berardi from suspension, though they remained without several injured players.
The visitors struck early, as Berardi continued his remarkable scoring record against Milan with his 12th goal versus them. Kristian Thorstvedt dispossessed Jashari in midfield before the ball was worked across for Berardi to curl a precise first-time effort into the far corner.
Mike Maignan soon kept Milan in the game with a sharp one-handed save to deny M’Bala Nzola on the break. Both sides had penalty appeals dismissed, with Laurienté and Nkunku going down under minimal contact.
Milan squandered a huge chance to equalize when Rafael Leao fired wide with only the goalkeeper to beat after latching onto a defensive mistake.
Their task became even tougher when Fikayo Tomori was sent off for a second booking after bringing down Laurienté on the counter, leaving Milan a man short for the majority of the match.
Sassuolo capitalized shortly after the restart, doubling their advantage through Laurienté, who combined neatly with Thorstvedt before drilling a low finish into the near corner.
Further chances came and went, with Nzola and Thorstvedt unable to find the target, while bookings were issued for simulation to Ruben Loftus-Cheek and Alieu Fadera.
The defeat leaves Milan under pressure in the race for Champions League qualification, while Juventus could draw level on points in third place with a win over Hellas Verona.
Alarmingly, Milan have now failed to score in five of their last seven matches.
