Antonio Conte's side is potentially out of the title-race after a 10-man Bologna side defeated Inter 2-1 on Sunday.
Inter Milan's Scudetto hopes were only left with theoretical possibility after being overturned by Bologna's 2-1 victory, while Lorenzo Insigne's winner helped Napoli beat Roma 2-1 at San Paolo.
On Sunday, Inter were fresh from a 6-0 victory over Brescia in the midweek but couldn't ride the momentum as they fumbled a 1-0 lead while Lautaro Martinez saw his penalty saved.
Romelu Lukaku put Inter in front in the 21st minute with a tap-in after Lautaro's twisting header hit the upright.
The away side was dealt a blow in the 57th minute as Roberto Soriano was sent off for insulting the referee.
The Nerazzurri wasted a golden opportunity five minutes later as Bologna's goalie Lukasz Skorupski played heroics to perform a double-save to deny Lautaro's spot-kick and Roberto Gagliardini's follow-up.
Inter were punished later as Musa Juwara smashed in the equaliser in the 72nd minute, four minutes before Inter's defender Alessandro Bastoni also saw red.
The game culminated in the 80th minute when Bologna completely turned around the match with Musa Barrow's first-time volley in the box.
Inter sit third with 64 points on the table, 11 behind the leaders Juventus. The Beneamata are effectively out of the race for the Serie A title.
In a showdown between the fifth-placed and six-placed sides, Napoli leaped over Roma with a 2-1 home victory while the Giallorossi's young talent Nicolo Zaniolo returned to the pitch after damaging his ACL in February.
Henrikh Mkhitaryan's scorcher on the hour mark wiped out Jose Callejon's opener, but it was Insigne that sealed the matters in the 82nd minute when he unleashed a curler that flew into the corner with a wicked swerve.
Atalanta continued their winning streak with a 1-0 away victory over Cagliari. The Dea now ranks fourth, only one point behind Inter.
In other games on Sunday, Sampdoria crushed SPAL 3-0, Brescia beat Hellas Verona 2-0, Parma suffered a 2-1 home defeat to Fiorentina while Udinese shared the spoils with Genoa in a 2-2 draw.
