Han fired a 5-under-par 67 to take a one-shot lead over Paula Creamer after the first day of this season-ending event. Han's round included a chip-in birdie at 18, but she only escaped with the lead after defending champion Annika Sorenstam stumbled down the stretch.
Controversy surfaced at the 18th hole while rules officials attempted to discern where Sorenstam, playing in the final group with Creamer, should hit her second shot after her drive plugged into a fairway bunker.
The ball landed outside of a red hazard line -- just shy of water on the right side -- and the debate was about whether or not Sorenstam's drive had crossed the hazard line at a point that would allow her to take her next shot from the drop zone behind the trap.
Creamer was involved in the discussion and looked uncomfortable being so. An elderly scorer was also asked about the shot, but he seemed to think that her ball had landed in the water.
After a 20-minute delay, the official on site ruled that Sorenstam could hit from the drop zone. It was the ruling Sorenstam was looking for, but she could only reach the front of the green with her third shot and finished the round with a double-bogey 6.
It was a disappointing finish to what could only generously be described as an up-and-down back nine for Sorenstam, a three-time champion who hit every fairway on the front nine to take the lead at minus-5.
Sorenstam began showing chinks in the armor when she landed in a bunker at the par-4 10th and settled for her first bogey of the day, which trimmed her lead to one shot.
That lead became two strokes again when Sorenstam drained a 20-foot birdie putt at the 11th to get back to 5 under, and she still led by two strokes after rolling in a 20-foot birdie putt at 13 to reach minus-6.
Things fell apart briefly for Sorenstam at the 14th, where she landed deep in a greenside bunker and struggled to a double-bogey 6. That tied her with Han for the lead, but it was a deadlock that wouldn't last long.
Sorenstam rebounded at the par-5 15th by striking a 7-wood within 12 feet to set up an eagle putt, which she drained to get back to 6 under.
But at the par-4 16th, she landed her approach shot behind a bunker and, despite a good chip within 6 feet, missed her par putt to fall into a tie with clubhouse leader Han at minus-5.
After a routine par at 17, the drama at 18 unfolded while the sun began to set at Trump International Golf Club.
There was less drama for Han down the stretch. She made par from 45 feet at the par-3 17th before chipping in from the greenside rough at 18 for her sixth birdie of the round.
Creamer, who is the LPGA's No. 2 money winner behind Sorenstam, mixed six birdies with a double-bogey at the par-3 seventh.
Catriona Matthew is alone in seventh place at 2-under 70, one stroke ahead of Heather Bowie and Candie Kung, who share eighth place after first-round 71s.
Christina Kim, last week's winner at the Mitchell Company Tournament of Champions, is tied for 10th place with two-time champion Karrie Webb, Lorie Kane, Birdie Kim and Meena Lee. That group is at even-par 72.
Sorenstam's collapse may not have been the worst of the day. Christie Kerr ended her round with a quadruple-bogey at 17 and a bogey at 18 to finish with a 4-over 76.