Abel Kirui denied fellow Kenyan Dickson Chumba a second successive Chicago Marathon victory, but Florence Kiplagat successfully defended her title.
Two-time world champion Kirui came out on top in a tight race in the Windy City, moving clear of Chumba in the final mile to win by just four seconds.
The time of two hours, 11 minutes and 23 seconds was far from his personal best, but it proved enough for victory on his first appearance at the Chicago Marathon.
Gideon Kipketer finished 58 seconds back in third position, with Paul Lonyangata and Stephen Sambu completing an all-Kenyan top five in the men's event.
The top four in the women's race were also from the African nation, with Kiplagat securing the win by a margin of one minute and 56 seconds.
It continues an impressive season for Kiplagat, who has also won the Berlin Marathon on two occasions, with the winning time of two hours, 21 minutes and 32 seconds improving upon a third-place finish in London.
Edna Kiplagat beat Valentine Kipketer to second, the latter replicating her brother Gideon's result by finishing third.
Purity Rionoripo was fourth across the line, with 2015 runner-up Yebrgual Melese completing the top five.