Lukaku converted a penalty in stoppage-time as Inter moved back to the top of the table, albeit briefly as Juventus won the Derby della Mole against Torino.
Inter are the only side in Europe’s big-five leagues to have won every game thay have played away from home so far this season.
Antonio Conte named a young Inter side for the trip to Bologna.
The Italian giants trailed 15 minutes from time, but Lukaku scrambled the ball home from a conrner to level.
And when strike partner Lautaro Martinez won a penalty in time added on, the former Manchester United man stepped up to slot home from 12 yards and secure a ninth win in eleven games.
Lukaku has begun the season in fine fettle after struggling for form and fitness at Old Trafford last year.
Ronaldo was named Serie A Footballer of the Year in 1998 and finished the season in question with 25 league goals.
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