Kirui, who has battled a litany of injuries since winning silver at the 2012 London Olympics, clocked 2hrs 11min 23sec with Chumba second in 2:11:26 and Gideon Kipketer third in 2:12:20.
"I was putting in my prayers and efforts in winning today," said 34-year-old Kirui. "I had a very strong mind, this time I knew it was a matter of life and death. The course favoured me and I was lucky that the weather was not so humid."
While Chumba was unable to repeat his 2015 triumph, Kenya's Florence Kiplagat won her second straight Chicago crown, powering to a dominant victory in 2:21:32, almost two minutes ahead of runner-up Edna Kiplagat's 2:23:28.
Valentine Kipketer, sister of Gideon, completed the Kenyan women's sweep, finishing third in 2:23:41.
In a men's race that in the absence of a pace-setter featured erratic surges in speed, a trio of Kenyans, Chumba, Kipketer and Kirui, broke away late from a group of 13.
With two kilometres remaining Chumba and Kirui had separated themselves and were jockeying for the lead before Kirui, running in Chicago for the first time, made a decisive move.
"It’s wonderful, amazing," said Kirui, who was embraced by training partner Kiplagat after the women's winner crossed the finish line.
Her dominant display ensured there was no finish-line drama in the women's race, in which a tight-knit leading group set a more methodical pace through the first two-thirds of the race than the top men managed.
With two kilometres remaining Chumba and Kirui had separated themselves and were jockeying for the lead before Kirui, running in Chicago for the first time, made a decisive move.
"It’s wonderful, amazing," said Kirui, who was embraced by training partner Kiplagat after the women's winner crossed the finish line.
Her dominant display ensured there was no finish-line drama in the women's race, in which a tight-knit leading group set a more methodical pace through the first two-thirds of the race than the top men managed.
