First Motherwell, then Rangers, blinked in a rare, four-team title race and now the focus was on just two contenders going head-to-head.
Surprise leaders Hearts had at one point been eight points clear, but having emerged from a haphazard season pock-marked with drama, Celtic have gradually eaten into that lead under O'Neill.
While both sides came into the game unbeaten in seven, Hearts had won just once in five on the road and it was that relative fragility that was to be their undoing.
Swept to victory by all but 750 of the 60,000-capacity crowd, Celtic's fifth home win in a row cemented their place as champions.
O'Neill's side won their final seven Premiership matches - their longest run of the campaign and their longest streak to finish the season since 2010.
Celtic had only won the title three times from eight when they started a final-day decider in second place, but they were not to be denied a 14th crown in 15 years.
O'Neill now leads his side to Hampden, where they will be strong favourites to complete the double against Dunfermline Athletic in the Scottish Cup final.
Hearts will look with anger at a penalty wrongly denied - according to referees' chief Willie Collum - in Saturday's draw with Motherwell, and the penalty award for Celtic at Fir Park which McInnes described as "disgusting".
They can, however, take some comfort from going so close - and splitting the Old Firm - in the first season of what Tony Bloom said was a 10-year project when the Brighton & Hove Albion owner invested in the Edinburgh club last summer.