Lewis said earlier if she wins, she would donate all her prize money to the Hurricane Harvey flood victims in Texas.
Lewis donates all of her winnings to the Hurricane Harvey Houston Relief effort.
Stacy Lewis hasn't hoisted an LPGA trophy since the 2014 WalMart NW Arkansas Championship, but she found her mojo and ended that long, painful winless streak at the Cambia Portland Classic Presented by JTBC.
"I've been motivated for one, but I've just been extremely calm", said Lewis.
Chun has a two-round total of 10-under 134 which leaves her in a three-way tie with 19-year-old Canadian Brooke Henderson, who shot a five-under 67, and veteran American Stacy Lewis who had a bogey-free 64. She won her 12th LPGA title for those suffering from the epic rainfall and deadly flooding that destroyed so many homes and businesses in Houston.
Chun's 68 followed a 66 on Thursday as she seeks her first win of 2017 after four runner-up finishes. A trio of golfers are just two shots back heading into the weekend including Jodi Ewart Shadoff, Ai Miyazato - who is playing in her final LPGA Tour event on USA soil prior to retiring, and Moriya Jutanugarn. There has just been a calmness about me this week.
"I wrote down a 2 on the scorecard before she even hit her putt because I knew she was going to make it", Lewis said. Lewis' husband, Gerrod Chadwell, is the head women's golf coach at the University of Houston.
If she can hold on to her lead on the final day she would collect the winner's cheque of US$195,000 (S$264,750).
"We're going to be able to help people rebuild houses and get their homes back". Lewis closed out with a two-putt par at the last.
Miyazato admitted she got emotional on the final hole of the tournament, and reflected on what she was going to miss the most about playing on the LPGA Tour. "Seems to be working so far", Henderson said.
Lewis also called on her fellow LPGA Tour pros to grab an extra pair of shoes when they next go shopping and she would hand them over to those in need. She played well in that run, stacking up 12 second-place finishes and winning more than $4 million, but she couldn't break through to win until finding some special motivation in Portland. She entered the week ranked 18th in the world.