Inter are now level on points with Juventus at the top of Serie A after they failed to overcome Fiorentina, who equalised in stoppage time.
Dusan Vlahovic scored a spectacular late equaliser as Fiorentina fought back to draw 1-1 with Inter and hand Juventus a boost in the Serie A title race.
Borja Valero's early strike against his former club looked set to be enough to claim the points for Inter, who had temporarily fallen into second place due to Juve's comfortable win over Udinese earlier on Sunday.
However, having seen a goal ruled out by the VAR before squandering several gilt-edged chances, Antonio Conte's side were unable to double their lead.
Fiorentina took full advantage as teenager Vlahovic stepped up with a sensational solo strike in stoppage time to secure a lifeline for under-pressure coach Vincenzo Montella while ensuring Inter could only move level on points with Juve at the top.