Mo Farah broke the European record in the Chicago Marathon.
The 35-year-old, who was third in this year's London Marathon, secured a new European record with a time of two hours, five minutes and 11 seconds.
Farah, competing in his first marathon in the US, burst clear of Ethiopia's Mosinet Geremew in the final half-mile in damp conditions in Illinois.
He is the first British man to win the Chicago race since Paul Evans in 1996.
Farah, a six-time world champion and double Olympic champion at both 10,000m and 5,000m, retired from the track in August 2017 to focus on road racing.
In London in April he clocked 2:06.21 to beat Steve Jones' 33-year-old British record, while last month he won a record fifth successive Great North Run.
Farah's former training partner and defending champion Galen Rupp recorded the same time as Farah posted in London in finishing fifth in Chicago on Sunday.
"It was great to run with Galen, who won last year, then to be able to come back and win it for myself," said Farah, who ran 2:08:21 on his marathon debut when finishing eighth in London in 2014.
"The conditions weren't great and everyone was thinking about conditions rather than time, but towards the end we picked it up.
"I felt good towards the end of the race. At the beginning I felt a bit sluggish but overall I'm very happy with it."
Kenya's Brigid Kosgei, runner-up in London and also in last year's Chicago race, captured the women's title in 2:18:35.
Daniel Romanchuk won the men's wheelchair race in 1:31:34, with Britain's David Weir third 1:31.43, while Manuela Schar took the women's wheelchair race in 1:41:38.