The Kenyans are back in Boston after a relative lull that saw them shut out in the world's most prestigious marathon twice in the past three years.
More surprisingly, so are the Americans.
Geoffrey Kirui won the 121st Boston Marathon on Monday, pulling away from three-time US Olympian Galen Rupp with two miles to go to give Kenya its first men's victory in five years. Edna Kiplagat won the women's race to complete the Kenyan sweep.
They were followed closely by Americans who grabbed two of the top four women's spots and six of the top 10 for men – the first time that's happened since the race went professional in 1986.
"It's so exciting to see Americans being competitive here," said Mr. Rupp, the Olympic bronze medalist who was making his Boston debut. "It's a real exciting time. And it's awesome to see American distance running on the upswing and being competitive in these races."
Mr. Kirui finished in 2 hours, 9 minutes, 37 seconds to claim the silver trophy, a guilded olive wreath from Marathon, Greece, and the $150,000 first prize. Rupp was 21 seconds back, and Japan's Suguru Osako 30 seconds behind him.
Rounding out the top 10 were runners from California, Arizona, Colorado, Oregon and Utah.
"American distance running is looking good today," said sixth-place finisher Abdi Abdirahman, a Somali immigrant and Tucson resident who is a four-time Olympian. "We have the podium for both men and women, so the future is great."
Ms. Kiplagat finished in 2:21:52 to win her Boston debut, adding the victory to two world championships and wins in London, New York, and Los Angeles. She pulled ahead of Rose Chelimo of Bahrain in the Newton hills to win by 59 seconds.
American Jordan Hasay, making her first run at the 26.2-mile distance, was third and Desi Linden was fourth – the first time since 1991 that two US women have finished in the top four.
"It keeps happening. We keep getting closer. We're putting more numbers in there and it's just a matter of time," said Ms. Linden, the 2011 runner-up by 2 seconds. "When Americans break the tape, it's going to be a big deal here."
Kenya had won either the men's or women's race every year since 1991 before being shut out in 2014 and again last year. In fact, Kenya had taken both titles six times since 2000, so dominating the top 10 that Boylston Street began to look like a Great Rift Valley training run.
But Ethiopia has surpassed its East African neighbors on Patriots' Day the past four years, earning its first sweep in 2016. Then, in December, Kenyan Rita Jeptoo was stripped of her 2014 title for failing a drug test and it was handed instead to Ethiopia's Buzunesh Deba.
For Kirui, even when he was running shorter distances, he had his eye on Boston.
"In my mind, I was sure that one day I would win this race," said Kirui, 25, who was running just his third marathon. "To come here to Boston, I knew I was going to face my colleagues who have run many times here.... I knew I would challenge some of the champions who have been competing here."
The American drought reached more than three decades from the time Greg Meyer won in 1983 until Meb Keflezighi ran down Boylston Street to raucous chants of "U-S-A!" in 2014, the year after the finish line bombings killed three people and wounded more than 260 others. (No US woman has won since 1985.)
Mr. Keflezighi, 41, said he plans to enter the New York Marathon, which he won in 2009, one last time in the fall before retiring. In his last competitive Boston run, he finished 13th in 2:17:00 despite pain in his quad muscles.
"The crowd got me through the finish line," he said.
Also running on Monday was Ben Beach, who completed the race for an unprecedented 50th time in a row. And Kathrine Switzer, wearing the same bib number – 261 – that she wore when she entered the all-male race 50 years ago.
The warm temperatures that hit 79 degrees at the 20-kilometer mark in Natick slowed the runners, but the strong tailwind was a boost – especially in the wheelchair races.
Marcel Hug won Boston for the third time, outpushing 10-time champion Ernst Van Dyk down Boylston Street and finishing in 1:18:04 to beat the course record and world best by 21 seconds. Fellow Swiss Manuela Schar shattered the women's mark by more than five minutes, winning in 1:28:17.
The winners' times on the point-to-point Boston course are considered a world best and not a world record because of the possibility of a supportive tailwind like the one on Monday.
"The wind is so important," Mr. Hug said. "The roads were good. Everything was fantastic today."
Earlier Monday, city officials announced plans for memorials to mark the sites where two bombs exploded during the 2013 race.
Also in the field was Boston Police Commissioner William Evans, who ran for the 18th time in 2013 but has skipped the races since the bombings so he could be available in case of another emergency. Evans, who completed his 52nd marathon overall, said he wanted to show that Boston is back to normal.
"If I can come back," he said, "everyone can."