"I could say right now, yes, I will be back here until I win it," the 32-year-old three-time Olympian told reporters after finishing the race in two hours, 22 minutes and two seconds, more than three minutes faster than her previous best but also three minutes behind Kenyan victor Rita Jeptoo.
Flanagan, who grew up in Marblehead, Massachusetts, closer to Boston than the marathon's starting line in Hopkinton, said she had desperately wanted to win Monday's race to honour the victims of last year's fatal bombing attack at the finish line.
"It does mean a lot to me that my city is proud of me," said Flanagan, who currently lives in Portland, Oregon. "I'm proud of how I ran and, like I said, I don't wish it were easier. I just wish I were better. It was a really heartfelt effort today."
Flanagan led the women's pack for the first 20 miles of the 26.2-mile (42.2-km) race, pushing a fast pace that set the stage for Jeptoo to break a 12-year course record.
Jeptoo acknowledged to reporters after the race that Flanagan's early pacemaking helped with the record.
"My body responded," said Jeptoo, who marked her second consecutive Boston Marathon victory on Monday.
Flanagan said she had thought that her early pacemaking would have caused more of her rivals to drop back.
"I'm honestly surprised how many women went with me today," said Flanagan. The second fastest U.S. finisher, Desiree Linden of Rochester Hills, Michigan, finished in 10th place, a little under two minutes behind Flanagan.
While American runners including Ryan Hall have drawn criticism in recent years for going out too fast in the early miles of the race and not being able to hold the pace to the finish, Flanagan said she had run according to her plan.
"My coach told me I was ready to do 2:22 today. It just wasn't fast enough," she said.
Flanagan, who finished fourth last year and said she was the first elite athlete to call and ask to run this year's race following the bombing attack, said she was overwhelmed by the turnout and energy of fans along the sidelines of this year's race.
"It was so loud that my ears almost hurt," she said.
(Editing by Frank Pingue)