'It's been a long time,' said Dunn, who earned $150,000 for the win. 'I always believed it would come. That's what got me here.'
Young-A Yang, who shared the lead entering the final round, posted a 4-under 68 to take second place at 10-under-par 206. Leta Lindley used a Sunday 66 to take third place at minus-9, while Laura Diaz posted a final-round 69 to end the tournament at 8-under-par 208.
Dunn opened her round with a 15-foot birdie putt at the first to get to 6-under. After a trio of pars, she dropped in a birdie putt at the par-5 fifth. The 32-year-old Dunn came back with a birdie at the eighth from 15 feet out.
The 10-year pro then stumbled to a bogey at the par-3 ninth when she was unable to get up-and-down for par. Dunn atoned for that error with a short birdie at the 12th. She came right back to birdie the 13th from inside 4 feet to get to minus-9.
Dunn turned it on down the stretch. She sank a 3-foot birdie try at the par-3 15th to grab a share of the lead. Dunn came right back at the 16th to take the lead by sinking an 18-foot birdie putt.
Dunn, a three-time runner-up, moved two shots clears of the field with a birdie from 5 feet out at the 17th. She parred the closing hole for career win No. 1 in her 245th career start.
'I've been playing really well. I'm happy with my swing and my ball striking,' Dunn said. 'The funniest thing is I bought a putter on Thursday night and put it in play on Friday. We just went to a golf shop and we were goofing around and I couldn't leave without buying something.'
Dunn putted out the final hole just after lightning flashed across the sky. There had been a two-hour, 40-minute weather delay earlier in the round, first due to thunder and lightning, then because of rain.
Yang moved to 7 under with a 5-foot birdie putt at the third to open her round. However, she tripped to a three-putt bogey at the next hole. The Korean dropped in consecutive birdies from the eighth to get to minus-8.
The 25-year-old Yang opened the back nine with three straight pars. She converted a birdie at the par-5 13th and came right back to drain a 26-foot birdie try at the 14th to move to 10 under. Yang could only manage to par her final four holes to take second place.
'I'm very pleased with the way I played, 4 under today is not a bad score,' said Yang. 'Before the day started, I said if I got it to double-figures under par I'd be very happy. I did that. Moira just played better than I did.'
Michelle Estill, who shared the second-round lead with Yang, posted a 1-under 71 to end the tournament at 7-under-par 209. Katherine Hull fought back from an opening-round 76 with rounds of 66-68 to take sixth place at 6-under-par 210.
Anna Acker-Macosko and Catherine Cartwright ended one stroke behind Hull at minus-5. Donna Andrews (70) and Tina Fischer (69) shared ninth place 3-under-par 213.