It's the first time the country has swept the men's and women's titles in this historic event, the world's oldest annual marathon.
Hayle won the elite men's division in an unofficial time of 2:12:45, completing a podium sweep by three men's runners from Ethiopia. He pulled away late from the 2015 champion, Lelisa Desisa, with a little more than a mile to go. Desisa finished second in a time of 2:13:32. Yemane Adhane Tsegay finished third in 2:14:02.
With a late charge on the women's side, Baysa came from behind to win her division in 2:29:19. Baysa, who was 37 seconds behind the leaders at mile 21, seemingly came out of nowhere to take the lead. At mile 24, she was by herself with the race in hand.
Through a translator, Baysa told WBZ
that she is "very happy" and "very lucky."
"To win Boston is not easy," she said.
Tirfi Tsegaye of Ethiopia was second in 2:30:03, while Kenyan Joyce Chepkirui was third (2:30:50).
American Tatyana McFadden won the women's wheelchair division for the fourth consecutive year, while Marcel Hug of Switzerland won the men's wheelchair race, defending his 2015 title.
While she crossed the finish line with no other competitors in sight, McFadden didn't lead the entire way. She admitted after the race in an on-air interview on NBC Sports Network that she got nervous around the fifth or sixth mile before taking the lead in mile nine.
"I just wasn't catching the rest of the pack as fast as I wanted to," McFadden said. "But you know what? I just needed to remember why I was running, to stay relaxed. The race is 26.2 (miles), and it's a long way to go."
The top American male finisher was Zachary Hine, who finished 10th in 2:21:37. The first American to cross for the women was Neely Spence Gracey, who finished ninth in a time of 2:35.
Marathon bombing survivors take part
The 120th running of the historic race took place under heavy security, three years after double bombings near the finish line left three dead and at least 264 injured.
Leading off this year's marathon were the mobility impaired runners, which included bombing survivor Adrianne Haslet. A professional ballroom dancer, Haslet lost a leg in the bombing three years ago. She is one of 21 survivors competing in this year's race. It's her first time running a marathon.
After about 10 hours of running, she stepped across the finish line on her prosthetic leg and lifted her hands in triumph. Buoyed by the people of Boston who cheered her on, she even got a shout-out from President Barack Obama whose account tweeted: "Terror and bombs can't beat us. We carry on. We finish the race!"
In a special moment last year, Haslet's two brothers ran the race, and she joined them at the finish line. On Friday, she threw out the ceremonial first pitch at Fenway Park before the Red Sox played the Toronto Blue Jays.
Haslet wasn't the only survivor to get the honor at Fenway over the weekend. Patrick Downes, who lost his left leg in the 2013 bombings, threw out the first pitch to Red Sox designated hitter David Ortiz on Sunday. Jeff Bauman, who lost both legs in the bombings, threw out the ceremonial first pitch Monday.
Downes and Haslet both were running to raise money for people with physical disabilities.
"Adrianne thank you for being my inspiration!! #BostonStrong," said New England Patriots quarterback Tom Brady in a Facebook post Monday
McFadden: 'I got chills' from the crowd
Because it's an Olympic year, the best American marathon runners are focusing on training for Rio in August rather than this race. The U.S. Olympic marathon trials were in February in Los Angeles. Many of the top Americans are in Boston, although they didn't hit the pavement. That includes Meb Keflezighi, who was the first American to win the Boston Marathon in 31 years when he did so in 2014, and Shalane Flanagan, a Massachusetts native who has finished twice in the top 10 at the Boston Marathon. Both were at Fenway Park for the ceremonial first pitch on Saturday.
Around 30,000 people registered for the race. The 26.2-mile course starts in Hopkinton and passes through Ashland, Framingham, Natick, Wellesley, Newton and Brookline before reaching the finish line on Boylston Street in Boston. Up to a million spectators lined the streets to watch and cheer.
McFadden said this is one of her favorite races because of how it's supported by the Boston community.
"Coming down the last mile, I got chills, literally goosebumps all over my body," McFadden said. "The crowd was electric today, and that's just what I needed."
Because of the 2013 bombings, as well as previous terrorist attacks in Brussels and Paris in the last six months, security was tight Monday.
For the third consecutive year, a number of government agencies and universities offered comprehensive training for public safety personnel supporting the Boston Marathon. They included the Massachusetts Emergency Management Agency (MEMA), Massachusetts State Police (MSP), Massachusetts Department of Fire Services (DFS), Massachusetts Department of Public Health (DPH), Boston Police Department, U.S. Department of Homeland Security (DHS), National Bomb Squad Commanders Advisory Board, New Mexico Tech, Texas A&M Engineering (TEEX), and Louisiana State University.
More than 500 police officers, firefighters, emergency medical technicians (EMTs) and paramedics attended these training courses leading up to the race, and over 1,800 individuals have been trained over the past two years.