PORTLAND, Ore. — Canadian Brooke Henderson won the Portland Classic by eight strokes Sunday to become the third-youngest champion in LPGA Tour history at 17 years, 11 months, 6 days. The third-round leader closed with 3-under 69 at Columbia Edgewater to finish at 21-under 267, the lowest total since the event went from 54 holes to 72 in 2013. Lydia Ko set the age record as an amateur in the 2012 Canadian Women's Open at 15 years, 4 months, 2 days. She also won the Canadian event in 2013 at 16, and won four times at 17. Lexi Thompson won the 2011 LPGA Classic at 16 years, 7 months, 8 days. Henderson's eight-stroke margin is the biggest on the tour since Jiyah Shin won the 2012 Women's British Open by nine shots. Last year commissioner Mike Whan denied Henderson's age petition, preventing her from playing in qualifying school to try to earn a tour card. Because she's assured of finishing among the top 40 in earnings this year, Henderson will earn a card for 2016.Pornanong Phatlum (68), Ha Na Jang (70) and Candie Kung (70) tied for second.