The Abingdon Marathon ended in controversy on Sunday when organisers disqualified the winner because he failed to enter the race officially.
Colin Paton, 33, from the British Army's Athletic Association, was first home in 2hrs, 34min and 41sec, knocking six minutes off his winning time last year.
The physical training instructor with the First Battalion Irish Guards thought he had made it two in a row in the marathon, rated third best in the country by Runner's World magazine.
But organisers of the race, now in its 24th year, decided to disqualify him because he was wearing race number 886, originally allocated to fellow soldier Carl Povey.
When Povey decided not to run with just a few days to go before the race, Paton took over his number, but failed to notify organisers before the 26-mile run around Abingdon and surrounding villages began.
After Paton was disqualified, first place was awarded to Trevor Hunter, who finished second out of 1,100 entries, and 750 runners on the day.
Paton said: "It's my own fault - I tried to get through to the organisers on the phone before the race to let them know but I couldn't get through. I suppose I should have sent an email.
"I ran a good race, but I'll just have to accept it - rules are rules, and that's life. I'll just have to come back and prove them wrong next year."
Hunter, 37, from Marlow, who finished 2.27.05, said: "I don't really want to take first place like this because Colin has run a great race and I have been well beaten, but I will accept first place reluctantly if that is what the organisers insist."
Philip Hailes, from Witney Road Runners, was second in 2.39.58, while Michael Aldridge, of Wootton Road Runners, was promoted to third in 2.40.50.
Announcer Ivor Hopkins said: "We didn't tell the crowd during the prize-giving that Paton had been disqualified, although some of them obviously realised something had happened.
"He knows he has made a mistake, and at least he had the satisfaction of actually winning the race."
Race organiser Gary Richards added: "Alarm bells started ringing when I saw him cross the line and realised he was last year's winner. I knew he hadn't been entered in the race."
"We have to stick to the rules because if a runner collapses and he is wearing someone else's race number, we could end up notifying the wrong family."
Race referee Barry Strange added: "The rules are there to protect the runners, so we have to stick to them.
"We can't understand how such an experienced runner has got himself in this situation."
Organisers said the race, which featured runners from nine nations including those from Abingdon's French twin town of Argentan, went smoothly apart from Mr Paton's disqualification. It was Mr Paton's 18th marathon and he has won three before.
Marie Synott-Wells was first woman home in 2.58.50 in 49th.
Runners for the Akzo Nobel-sponsored event were raising money for Sir Michael Sobell House at the Churchill Hospital, and See Saw, the Oxford-based charity that works with bereaved children.
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