But, officials said, it was a lie.
Frank Meza, 70, finished the marathon with an official time of 2:53:10, more than an hour ahead of the next closest person in his age group.
After an investigation, however, Meza was disqualified. Marathon officials said in a statement that cameras posted along the race capture Meza "re-entering the course from a position other than where he left it."
"The video evidence is confirmed by a credible eyewitness report and our calculation that Dr. Meza’s actual running time for at least one 5K course segment would have had to have been faster than the current 70-74 age group 5K world-record," the statement read, calling that an "impossible feat during a marathon."
Marathon officials say an image shows Meza stepping off a sidewalk and joining the race. Later, he's again spotted coming from a sidewalk and re-entering the race.
Meza, however, denies the allegations of cheating, saying he merely left the course in search of a bathroom, running on the sidewalk as he did so.
“I didn’t cut the course,” he told the Los Angeles Times.
The Los Angeles Marathon has offered to let Meza run the 2020 race with an observer alongside him.
“That’s my only silver lining,” he said.
It's not the first time Meza has been disqualified from a marathon. In 2014 and 2016, he was disqualified from the California International Marathon for irregular splits. He was then banned from the race.