Chumba broke up a tactical race with a surge after about 30km and gradually increased his lead over Kitwara.
"The race was good, but the pace was slow to 30km," said the 28-year-old, who won the Tokyo marathon in 2014 and finished third there this year.
Kenyan Sammy Ndungu took third in 2:10:06, followed by Ethiopian Girmay Birhanu Gebru and surprising American Luke Puskedra.
Kenya's world half-marathon record holder Florence Kiplagat claimed the women's race, breaking away at 40km to win in 2:23:33.
"The course for me was very nice," a smiling Kiplagat told reporters. "It was a flat course, sometimes it's windy, but that is part of competition."
Ethiopians Yebrgual Melese and Birhane Dibaba took the next two spots with Melese 10 seconds adrift of Kiplagat.
Early leader Kayoko Fukushi of Japan finished fourth, just one second behind Dibaba in 2:24:25.
Deena Kastor, aged 42, took seventh in a U.S. masters record 2:27:47.
NO PACE-SETTERS
The race was run without pace-setters for the first time in 26 years and it noticeably affected times and strategy on the flat, typically fast course with Chumba's winning time the slowest in eight years.
As many as 10 runners were in the lead pack through the first half of the race as Chumba, Kitwara and others let first-time marathoner Elkanah Kibet, a Kenyan-born American, set the pace. He finished seventh.
Only when Chumba made his move did the pace pick up with the Kenyan, Kitwara and Ethiopian Abera Kuma forming a group of three before Kuma, who was running his fifth marathon in 20 months, faded.
Most top American men and women skipped the race to prepare for February's U.S. Olympic marathon trials.
American Tatyana McFadden won the women's wheelchair race for a sixth time and Australian Kurt Fearnley took the men's event with McFadden and top U.S. men's finisher Josh George, who was third, qualifying for the 2016 Rio Paralympics.
(Reporting by Gene Cherry in Salvo, North Carolina, editing by Ed Osmond and Ken Ferris)
