Before the event began, Lewis announced she'd donate her earnings from the tournament to Hurricane Harvey relief efforts.
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 really feel like the last few months I've been playing some good golf".
Chun In-gee of South Korea, who started the day in a three-way tie for the lead, had three birdies and 15 pars for a three-under 69 that left her four shots off the pace.
Hurricane Harvey has killed around 50 people and unleashed massive flooding that damaged up to 50,000 homes in Houston.
It certainly wasn't an easy win, what with Chun breathing down her neck down the stretch.
Moriya Jutanugarn of Thailand and Brittany Altomare of Prattville, Alabama tied for third at 14-under.
"It has been so hard being away from home and my family the last week", Lewis said in a statement she posted on the social media website. "Anybody who has seen me play knows that's not normally me, but I haven't anxious about anything", said Lewis, whose husband is a golf coach at the University of Houston. "My caddie (Travis Wilson) has been here way more times than anybody probably in this field, and so I think we have an advantage as far as knowing the golf course".
Tied for the second-round lead with two-time defending champion Brooke Henderson and In Gee Chun, Lewis had eight birdies in a seven-under 65 to reach 17 under at tree-lined Columbia Edgewater in Portland. The people down there got it way tougher than us. She bounced back immediately, however, with a birdie on the very next hole. Chun missed a short birdie putt at the par-4 14th, and pulled to within a stroke with a 45-foot birdie at the par-3 16th.
First place pays US$195,000 and second pays US$120,000. She also broke through in Portland after finishing second twice - two strokes behind Suzann Pettersen in 2013 and four shots behind Brooke Henderson previous year. Her previous best in 2017 was a tie for 16th at the LOTTE Championship presented by Hershey, and now, she said, she's eager to play on bigger stages - including the Evian Championship, the LPGA Tour's final major of 2017. "It's nice to see yourself do that again".