In a widely-anticipated repeat of last month’s UK final, O’Sullivan raced into a 4-0 lead before Ding won three-in-a-row - including pocketing a sensational 147 break - to setup a tense finale.
The world number one then clinched the final two deciding frames to keep alive his bid to win a historic eighth Masters title.
"I was pleased to get over the line in the end," O'Sullivan told Eurosport. "My cueing is not great, but I tried. I tried, but sometimes there is nothing more you can do.
"I haven't played much since the UK. (I'm) a little bit tired, but that's part of the job. I must have gone through 20 different cue actions out there.
"When I say I don't care, I play like I play when I play down the club. I think you've just got to go for it, and play from a place of abandonment."
He will next face the winner between Neil Robertson and Barry Hawkins, who play on Tuesday evening.