Han finished three rounds at 12-under-par 201 for her first victory of 2005 and the fourth title of her five-year LPGA career. She ended two strokes clear of fellow Korean Soo-Yun Kang, who made her run with a 5-under 66 in the final round.
'I'm just pretty proud of myself,' said Han, who held at least a share of the lead after each round at Trump National Golf Club of Los Angeles.
Catriona Matthew shot a 3-under 68 in the final round to finish alone in third place at minus-8, while Natalie Gulbis (71) and Karine Icher (73) tied for fourth place one stroke further back.
Jeong Jang (74) and Katherine Hull (69) shared sixth place at 6 under, and Marisa Baena (71) was eighth at minus-5.
Defending champion Annika Sorenstam led a group of four players knotted in ninth place after a final-round 70. That group came in at 4 under.
Slow play on Friday and a long fog delay on Saturday combined to force the tournament to a Monday finish, and Han entered the day even-par through her first eight holes of the final round.
But the 27-year-old began distancing herself from the field with a birdie at her first hole Monday, the par-5 ninth. She knocked a sand wedge within eight feet there to make the turn at 10 under.
Han made it two birdies in a row at No. 10, where she again hit a sand wedge close (14 feet) to set up birdie and move to minus-11. She continued her bogey-free back nine with three straight pars after that, although she missed a 2-foot birdie putt at 13.
At the par-5 14th, Han moved two strokes ahead of Kang with her fourth birdie of the final round, knocking a gap wedge within 6 feet to set up her four.
Four straight pars to finish the round were good enough to win because Kang played her final four holes at even-par and missed a 6-foot birdie try at the 18th that would have at least given Han something to think about.
Han, who posted just three bogeys in the tournament during a week in which many players struggled, had said that she wouldn't like a Monday finish. But her feelings changed after the final round.
'Actually that's a pretty good thing because yesterday I was just waiting for five hours on the course and played like eight holes,' said Han, who collected $195,000 for her win. 'But this morning [I came] back pretty good, and started birdie, birdie. That's good for me.'
Tied with Sorenstam for ninth place were Kim Saiki (69), Young Jo (71) and Mi Hyun Kim (73). United States Solheim Cup members Rosie Jones (72), Beth Daniel (73) and Michele Redman (74) tied for 13th place at minus-3 with Shi Hyun Ahn (71).