The 24-year-old Njui overcame the hot weather and a one-and-a-half-minute deficit to win the men's race in two hours 11 minutes 22 seconds, beating compatriots Harun Njoroge Mbugua and Mekubo Job Mogusu.
Hara, running a full distance marathon for the first time in more than a year, spurted at around 32 kilometres to take the lead ahead of Hiroko Miyauchi before crossing the finishing line in 2:34:12.
Japan-based Kenyan Joseph Gitau set an early pace by taking the sole lead from the seven-kilometre point, but he was overtaken by Mogusu at around the 25km mark before Njui snatched the lead after passing the 32km point.
Mjoroge Mbugua came in second in 2:13:04 and Mogusu third in 2:16:38.
Among the women, Mizuho Nasukawa was left behind after passing the 22km point, leaving Hara and Miyauchi to leapfrog for the lead before Hara made a break away at the 32km point.
Miyauchi clocked 2:35:42 to finish second and Nasukawa 2:36:07 for third.
It was Hara's first victory since winning the Osaka marathon in January 2007.
"I can't believe it," said Hara. "I finally won again. I was able to come to the starting line, because so many people had supported me last year while I had to stay at home," said Hara, 28.
She failed to qualify for the world championship after finishing third in the 2009 Osaka marathon but has been working for the 2012 London Olympics.
Read more: Njui, Hara win Hokkaido marathon - Athletics - More Sports - Sports - The Times of India http://timesofindia.indiatimes.com/sports/more-sports/athletics/Njui-Hara-win-Hokkaido-marathon/articleshow/6455550.cms#ixzz0y0etiB3g
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