Boston's third marathon since its 2013 finish-line bombing has been won by Ethiopians, with Berhanu Hayle winning the men's and Atsede Bayse the women's race. Women's defender Caroline Rotich dropped out mid-way.
Hayle's win in a time of 2 hours 12 minutes and 45 seconds made it Boston's slowest men's marathon since 2007. His victory at the world's oldest annual marathon represented his biggest career win to date.
The 21-year-old had previously won marathons in Dubai, Zurich and Warsaw.
Crossing over the Massachusetts Turnpike, Hayle pulled away from defending men's champion Lelisa Desisa, the race's early pace-setter who finished second.
LIke Hayle and Desisa, the third home was another Ethiopian: Yeman Adhane Tsegay.
Ethiopians also dominate women's race
Baysa's winning women's time was 2:30:03. She pulled from behind in the closing 8 kilometers (5 miles) to finish 44 seconds ahead of fellow Ethiopian Tirfi Tsegaye.
The lone Kenyan to win a medal was Joyce Chepkirui who finished third in the women's race.
Defending women's champion Caroline Rotich of Kenya dropped out after only 8 kilometers with what looked like an ankle problem.
The men and women's winners this year each receive $150,000 (133,000 euros).
Approximately 30,000 runners took part in Boston's prestige event, with 5,000 law enforcement officers on hand, in cool clear windless conditions.
At the finish line in 2013, twin bombings killed three spectators and wounded more than 260 others.
2013 victims race using artifical limbs
One of two assailants, Dzhokhar Tsarnaev, now 22, was convicted last year and sentenced to death. His 26-year-old ethnic Chechen brother died in a shootout shortly after the bombings.
Two people who lost limbs in 2013 took part in this year's event. Adrianne Haslet and Patrick Downes were fitted out with special carbon-fiber blades.
ipj/msh (AFP, dpa, Reuters, AP)