Ryan Hall takes second at the annual run in San Francisco.
It will be the American marathoner's second race of the 2013 season.
It will be his first race this year.
Kenyan is a dark horse to win Monday's race.
30-year-old American is in the midst of a comeback, and he hopes his hard work pays off in Boston.
The fastest American marathoner of all time has a quad injury.
He expects to be at the level of rivals Mo Farah and Galen Rupp.
Forty eight athletes from 14 countries will take part.
The race will include five of the six marathoners from the 2012 U.S. Olympic team.
A huge bonus is up for grabs in the half marathon.