In the men’s race, Galen Rupp became the first American in 15 years to win, beating Kenya’s pair of Abel Kirui and Bernard Kipyego, who came in second and third respectively.
It was only the fourth career start at the 42.16km distance for Rupp, who was second in April’s Boston Marathon and third in last year’s Rio Olympics, and just the third marathon for Dibaba, a former world and Olympic 5,000 and 10,000m champion.
“It’s just incredible,” Rupp said.
“You train so hard to have a race like this and to have it all come together, words just can’t describe the feeling when I came across the line. It’s just a great day.”
Rupp surged ahead for good with three miles remaining to win in 2hrs 9mins 20secs with Kirui, the defending champion, 28 seconds back and Kipyego, third in 2:10:23.
The halfway mark
Only one rival remained with Dibaba past the halfway mark as this year’s London Marathon runner-up cruised to victory in 2:18:31. defeating Kosgei by 1:51 with American Jordan Hasay third in 2:20:57.
“This is my third marathon and I’m very happy to have won here,” Dibaba said. “I worked very hard for this.”
Dibaba and Rupp each took a $100,000 top prize at the 40th anniversary edition of the classic, which saw more than 40,000 runners compete on the streets of the US Midwestern metropolis.
Rupp, 31, was the first American man to win the Chicago Marathon since Morocco-born Khalid Khannouchi in 2002. Kenyans had won the Chicago men’s title in 13 of the past 14 years.
Kenya’s Dennis Kimetto, world record holder from his 2014 Berlin Marathon triumph in 2:02:57 and the 2013 Chicago champion, led at the halfway mark in 1:05:49 but began limping soon after and by 25km was off the pace for good.
The lead pack slowly dwindled over the next 10km, leaving only Rupp, Kirui and Ethiopia’s Sisay Lemma after 22 miles.
Dibaba vowed to challenge the women’s course record of 2:17:18 set by British world record holder Paula Radcliffe in 2002 and was on that pace in the early going.
Dibaba led after 5km in 16:08, 19 seconds under Radcliffe’s course record pace, and had trimmed the field in the lead pack to only five.
Florence Kiplagat’s 10km time of 32:28 was also 19 seconds faster than Radcliffe’s record split but by 15km it was Hasay, third this year in Boston, leading in 49:02, three seconds under record pace.
Dibaba led at the halfway mark at 1:08:48, well off Radcliffe’s record pace, but made another charge that left only Kosgei on her heels. The Kenyan fell back with 10km remaining, leaving Dibaba alone to the end.
Dibaba, 32, is a two-time 5,000m world champion and three-time 10,000m world champion.
She won 5,000 and 10,000 gold at the 2008 Beijing Olympics and defended the longer crown four years later in London. Last year in Rio, Dibaba was third in the 10,000.
And Dibaba was second at the London Marathon in April in 2:17:56, becoming the third-fastest woman at the distance in only her second try.