Setting off as the 4-9 favourite, Enable rounded the home turn behind Sovereign but accelerated past after Dettori took a nonchalant look over his shoulder to see Japan toiling.
The John Gosden-trained super mare pulled clear and was never threatened, with Sovereign taking second place.
Last year, Enable became only the third dual King George winner, after Dahlia (1973 and 1974) and Swain (1997 and 1998).
Enable has been kept in training at the age of 6 for another attempt at a third win in the Prix de l'Arc de Triomphe in October.
“With Anthony Van Dyck not there, it was obvious Sovereign would set a solid pace, not a mad one,” Gosden said
“Given Japan has won a Juddmonte International over 10 furlongs, he was always going to ride him to beat us for toe, but it went perfectly.
“I'm always worried here when you get rain on quick ground, because they can lose their hind legs, but thankfully that didn't happen.
“Her work had been very good leading into this, and she was quite imperious today.
“It's a pleasure to see when Frankie's looking round, but if you do it too much you might fall off! She won it very nicely – I think he only gave her one flick.
“As they get older, they get more professional and think once they are two or three lengths clear they can ease up, but you never know if another horse is coming.”