Ronaldo’s low strike, following a back-heel from team-mate Miralem Pjanic, brought Juventus level at the San Siro.
Radja Nainggolan had given the hosts the lead with a spectacular 25-yard volley after Matteo Politano’s flick.
Ronaldo has now scored 27 goals for Juventus after five for Sporting Lisbon, 118 at Manchester United and 450 for Real Madrid.
Juventus may well have already won Italy’s Serie A title but that did not stop Inter fans from mocking their rivals.
Before Saturday’s game, Inter fans held up a mosaic that spelled out ‘game over’, a reference to Juventus’ shock 3-2 aggregate loss to Ajax in the quarter-finals of the Champions League earlier this month.
Nainggolan continued the party mood with a stunning volley to give Inter a first-half lead, but Juventus had the last laugh with Ronaldo’s 62nd-minute equaliser.
Juventus, who clinched the Serie A title with a 2-1 win over Fiorentina on 20 April, now hold a 21-point lead over second-placed Napoli.
The top four sides qualify for next season’s Champions League and Inter, who finished third behind Barcelona and Tottenham in this year’s group stage, are third in Serie A, six points clear of city rivals AC Milan in fifth spot.