Britain's Claire Hallissey secured the Olympic marathon qualifying standard by finishing sixth in Chicago.
The 28-year-old from Hertfordshire ran only her second marathon, in two hours, 29 minutes and 27 seconds - 93 seconds inside the UK Athletics requirement.
GB may select up to three athletes for the event, with one likely to be Paula Radcliffe, who ran
Jo Pavey and Mara Yamauchi are also likely to be chasing Team GB vests for the 2012 marathon.
Hallissey's impressive showing underlines the giant strides made by the Bristol-based runner in the last 12 months.
In her maiden marathon in New York last year, she clocked 2:36.12 when crossing the line as the 18th woman.
Russian Liliya Shobukhova (2:18.20) become the first person to post three straight victories in the Chicago event.
And Kenyan Moses Mosop led the men home in a course record of 2:05.37.