The Miami Herald said the 38-year-old film star, who lives in Miami, was a member of a relay team along with his stepfather Jay Jones and family friend Barry Hetherington.
"My brother talked me into it," Damon told the newspaper, referring to Kyle Damon, who finished 27th in Sunday's competition. A total of 960 people competed in the event.
Matt Damon's wife Luciana and their newborn daughter Gia were waiting for him at the finish line. He completed the 6.2-mile leg of the race in 59 minutes, 54 seconds, the Herald said.
"I was doing this movie this summer where I had to put on all this weight and my brother told me, 'Oct. 5, save the date,'" Damon said, recalling how he decided to take his brother up on his offer because "I've got to get in shape for the next thing I'm doing."
Asked once the race was over if more running is in his future, Damon quipped: "I don't think so. I knew I was in trouble when the old guy with the oxygen tank passed me."