Laura Davies finished alone in second at 8-under-par 280. Annika Sorenstam was one stroke further back at 7-under-par 281 alongside Rosie Jones.
'I had a great week. And I put it in the right places on the green, to allow myself to get some birdies, and stayed very focused out there today,' said Moodie. 'Annika and Laura are such great players and they could have come back very, very easily.'
Moodie was one of 39 players who returned to Mount Vintage Plantation & Golf Club early Sunday morning to complete the third round after play was suspended Saturday due to darkness.
The 28-year-old led by four at the start of the final round and began to pull further away from the pack with a birdie at the first. At the par-3 third, Moodie landed the ball 12-feet from the cup for another birdie.
'Believe me, I liked the cushion,' said Moodie. 'Once I got there I kind of knew I had to keep holding on. If I was making pars, they had to make birdies to get me.'
She reached 16-under with a two-putt birdie at the par-5 sixth before running into trouble with a bogey at the following hole. Moodie responded with a birdie at No. 8 to make the turn with a five-shot lead.
After Davies made back-to-back bogeys from the 10th, all Moodie had to do was close out the round.
Moodie climbed to 17-under with a 10-foot birdie putt at the 15th and coasted to the win despite a double-bogey at the par-4 17th.
The victory was Moodie's first since the 2000 ShopRite LPGA Classic.
'I never had any doubt,' said Moodie. 'I mean I've come so close so many times. I've just been knocking on the door.'
Sorenstam, who has three victories so far in 2002, earned her seventh top-10 finish in eight events.
Davies, a 20-time winner on the LPGA Tour, held the lead after the opening round but could not keep up with Moodie's feverish pace.
'We thought we had to shoot 65, and as it turns out that would have won by a shot,' said Davies. 'I don't really think 65 would have been good enough, because I think she would have stepped up to the plate and got one more herself.'
Full-field scores from the Asahi Ryokuken International Championship