Kenya’s John Korir survived an early tumble, ran away from the field in the Newton hills, and went on to a dominant victory in the 129th Boston Marathon on Monday morning, posting the third-fastest time (2 hours, 4 minutes, 45 seconds) in race history.

Korir, whose brother Wesley won here in 2012, finished fourth last year. But a victory in Chicago last fall in the second-fastest time in event history gave him confidence that he could prevail on a more challenging layout.

“If you believe in yourself you can make it,” Wesley told him, before they became the first siblings to win here.

On a cool day with a slight wind that was made for brisk times, the pack at the midway point was under the pace of the course record of 2:03:02 set by Kenya’s Geoffrey Mutai in 2011.

After falling shortly after the start, Korir recovered quickly, bided his time, and dashed away from the pack after 20 miles and was alone the rest of the way.

Korir won by 19 seconds over Tanzania’s Alphonce Felix Simbu and Kenya’s Cybrian Kotut. Korir’s time was the second-fastest by a Boston victor and third behind 2011 runner-up Moses Mosop.

Conner Mantz was fourth in the second-fastest time (2:05:08) by an American, behind Ryan Hall’s 2:04:58 in 2011.

John Powers can be reached at [email protected].