Paolo di Canio unwittingly completed the town's half marathon after losing his bearings on the fun run course.
The 43-year-old Swindon Town manager was supposed to sound the horn to start Sunday's main race before completing the two-mile short course.
But the Italian took a wrong turn and ended up finishing the full 13.1 miles in one hour 49 minutes - 36 minutes behind race winner Dave Roper.
"I couldn't stop, there was a challenge," he told BBC Wiltshire.
"There were three options, I thought I should start with the fun [run] marathon but unfortunately we changed direction, kept going and followed the first group.
"Unfortunately I ended up doing a full half marathon plus 800 metres.
"At the end I was very happy because I finished without stopping, even for one second. I wasn't ready but I never stopped running.
"I'm very happy but it was very tough."