BOSTON — Unsure until Monday morning whether she would attempt the 115th Boston Marathon, Joan Benoit Samuelson of Freeport completed the 26.2-mile course in 2 hours, 51 minutes, 29 seconds.

Samuelson’s back seized up Thursday morning after she spent the day in Boston leading stretching exercises – something she rarely does herself – at clinics for inner-city youth and then driving “white-knuckled” back to Maine in a driving rainstorm.

Nevertheless, “it was great to be back on the Boston course” after an absence of 18 years, she said in Copley Square after greeting her daughter, Abby Samuelson, who ran Boston for the first time.

Maine’s fastest finisher Monday was Robert Gomez of Saco, who completed his Boston debut in 2:24:18 to place 35th. Sheri Piers of Falmouth was the first Maine woman across the line, in 2:39:23, good for 24th in the women’s field.

Geoffrey Mutai of Kenya ran 2:03:02 to win the men’s race, which would be a world record but Boston is considered a downhill course and times are not eligible for world records. Nonetheless, Mutai’s time was the fastest ever.

In an exciting women’s finish, Caroline Kilel of Kenya held off two strong surges by Desiree Davila of Michigan over the final 800 meters to win by two seconds in 2:22:36.