Peter Bosz's men have been in pitiful form throughout their Group H campaign, and are already out of the running for a knockout spot.
And their woes were compounded early on at the Bernabeu when Ronaldo hit home shortly after Borja Mayoral opened the scoring to make it 2-0 to the hosts.
That goal meant that Ronaldo has scored in every single group game of the 2017-18 campaign, with a total of nine strikes so far.
No other players had managed that feat previously since the Champions League adopted its group phase in 1992-3, marking yet another record for the Portugal star.
It was the 32-year-old's 114th Champions League goal, extending his record as the competition's all-time highest scoring player.
While Ronaldo, who is the favourite to claim a fifth Ballon d'Or on Thursday, has proved prolific in Europe, he has scored just two goals in 10 La Liga appearances this season.
Ronaldo's goals in Europe, however, have not quite sufficed to seal top spot in Group H for his team.
Madrid went into their final game knowing they were guaranteed second place behind Tottenham and rested several stars against Dortmund - although ever-motivated Ronaldo was not among those left out.