Carter, seeking a first Triple Crown title, surged into a 6-3 advantage after taking the first frame of the evening session.
But O’Sullivan roared back, winning seven of the final eight frames to secure an eighth Masters crown and become the oldest ever winner of the event.
It represented a disappointing end to a fine tournament for Carter, who produced a record nine centuries across the week in London, but the 44-year-old was frustrated by the behaviour of some spectators.
With the crowd firmly behind O’Sullivan, who had criticised the venue this week, the referee had to warn fans not to shout out while the players were over shots.
“It’s hard enough to beat [O’Sullivan]” said Carter. “But when you’ve got people shouting when you are on your shot and saying stupid things at important times because half of them haven’t got enough brains, it’s ridiculous.
“There are some morons in the crowd. It is just unbelievable really. Ronnie played very well, he missed a few at the end and the crowd got excited. When you play Ronnie, you have to play the crowd, you have to accept it. I did my best but it just wasn’t good enough.”
O’Sullivan’s Masters triumph follows his UK Championship win in December, leaving him seeking only the World Championship to complete a single-season sweep of the Triple Crown events.
The 48-year-old has not previously achieved the feat, but will head to the Crucible in April as the heavy favourite.
Before then, though, O’Sullivan intends to take a break, playing in the World Grand Prix this week but then focussing on exhibition events.
“I’ll just swerve all the other tournaments now,” O’Sullivan said to Eurosport. “I feel like I want a break. I’m looking forward to getting on the exhibition circuit, start playing more exhibitions.
“I enjoy them, they’re a bit of fun. Too much intense snooker for me is not good. I need to back off and consolidate and get some fun in the game so the exhibitions will be good.”