Simone Verdi's stunning first-half strike grabbed a point for Bologna and wrecked Inter Milan's 100 percent start to the new Serie A season at the Stadio Renato Dall'Ara.
Verdi drove home the opening goal in the 32nd minute as his side dominated the first half before a late penalty from Mauro Icardi salvaged a draw for the visitors.
Inter must have expected to extend their winning start to the season to five straight wins against a Bologna side who had struggled to claim four points from as many games.
But the home side started in purposeful fashion with the dangerous Federico Di Francesco hitting the first shot on target from outside the box with just five minutes on the clock.
Former Milan youth player Verdi seemed intent on making an impression against his former city rivals and he forced a save out of Inter goalkeeper Samir Handanovic from a tight angle.
Erick Pulgar followed up with a long-range shot which went just wide and Verdi also had chances before Inter finally summoned a shot in the 24th minute through Yuto Nagatomo.
Bologna grabbed their deserved lead in the 32nd minute when Verdi was fed by Bruno Petkovic in midfield and ran at the Inter defence before drilling his shot past Handanovic from the edge of the box.
Di Francesco could have doubled the home side's lead before half-time and the match continued in the same vein after the break as Di Francesco and Verdi both missed further chances.
Inter gradually began to gain a foothold in the game with Antonio Candreva and Icardi both having shots blocked in quick succession as the visitors began to exert some pressure.
Brazilian Joao Miranda headed straight at Bologna keeper Antonio Mirante and second half substitute Eder flashed an effort wide as an increasingly desperate Inter laid siege to the home goal.
Finally the visitors made their breakthrough 15 minutes from time when Eder was fouled in the box and Icardi stepped up to fire home the penalty and make it 1-1.
With the home side flagging, Inter had a chance to extend their perfect record when a late chance fell to Ivan Perisic but the Croatian dragged his effort wide of target.