The two courses diverged at one point and Ahmed, who entered the 10K as an elite runner, went the wrong way to finish the half-marathon with a time of 1:03:08 -- nearly five minutes ahead of the competition.
"Rules are rules and in this case they say we have to disqualify Omar," Paul Foster, chief executive of The Great Run Company, was quoted as saying by the BBC.
"We salute his performance and he has been invited to take part in next week's Great Manchester Run as an elite athlete. Of course, we also look forward to welcoming him back to Bristol for 2022's Great Bristol Run."
As a result, Chris Thompson who finished with a time of 1:07:53 was adjudged the winner of Sunday's race.
The 10K and half marathon are usually held in different months. Both races were cancelled last year due to the Covid-19 pandemic.
