Cindy Figg-Currier, who shared the overnight lead with Han, struggled to a 2-over 73. She fell back to 6-under-par 207 and is one stroke ahead of Mi- Hyun Kim. Jennifer Rosales is one stroke behind Kim at 4-under-par 209 after a 2-under 69 Saturday.
Mallon started and closed in fine fashion while cruising through the middle of her round. She began three strokes behind the leaders and picked up a birdie at the first. She continued to close the gap with a birdie at the next.
The 40-year-old stumbled to a bogey at the fourth, but was able to recover that stroke at the par-4 eighth.
Mallon settled down from there as she ran off six consecutive pars. Then she really played some fine golf.
'The round started really nice,' Mallon said. 'I made one bogey today, which was a good bogey. Once I got through the middle of the round where I wasn't playing as well, I got it back late in the round.'
She knocked a 7-wood on in two at the par-5 15th and two-putted for birdie. She drained a four-foot birdie putt at the next for her fifth birdie of the day.
Mallon continued her run at the 17th where she made it three straight with a kick-in birdie from within one foot. She was not done either. She got up-and- down from right of the green at the par-5 18th to close her round with four straight birdies.
'I thought I had a good second shot there on 18,' Mallon said. 'It came out just how I wanted it to and ended about four feet above the hole. That was probably the hardest putt of all the holes I had. It was nice today to knock down the four or five-footers.'
Mallon is looking forward to the duel tomorrow with Han.
'It really should be the two of us tomorrow,' said Mallon. 'It's going to be fun. I like to know what the person in the lead is doing. I'm glad I'm playing with her.'
Han played steady golf to begin her day. She opened with five straight pars before stumbling to a three-putt bogey at the par-4 sixth. She came back to even par for her round with a birdie at the par-4 ninth.
The South Korean moved to 10-under with birdies at the 11th and 13th. She advanced to minus-11 when she converted a 35-foot birdie putt at the par-5 15th.
Han dropped a shot at the next, but grabbed a share of first place with a two-putt birdie at the last.
'It was a little windy today,' Han said. 'But my putting was good and my shots were fine. I felt really confident with my putting today.'
Kim Williams and Audra Burks share sixth place at 3-under-par 210.
Beth Daniel, who won the Canadian Women's Open last week, and defending champion Gloria Park are among six golfers tied at 2-under-par 211. Also standing at 2-under are Michele Redman, Stephanie Louden, Joanne Mills and Grace Park.
Suzy Whaley, who will tee it up at the PGA Tour's Greater Hartford Open next weekend, posted her second straight 4-over 75 to fall to 6-over-par 219.