The 35-year-old Purcell completed the 26-mile, 385-yard course from Two Harbors to Avalon in two hours, 50 minutes, 22 seconds, according to unofficial results supplied by race organizers. John Tribbia, 29, of Boulder, Colo., was second in 2:50:48.
Latham, 42, was timed in 3:45:38, 38:38 slower than the women's record time of 3:07 set in last year's race by Heather Fuhr. Sharon Pevsner, 42, of Sierra Madre, was second in 3:49.09.
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The course covered 23 miles on dirt trails, where the island's feral buffaloes graze, that are usually inaccessible to the public, said Jack Caress, owner of Pacific Sports LLC, which conducted the race.
The course also included numerous hills and a 1,600-foot climb in elevation, Caress said.
A field of 1,100 runners from 44 states and 13 foreign countries -- including Afghanistan, Brazil, Canada, China, Norway and the United Kingdom -- entered the race, Caress said.
County fire officials said no major injuries were reported during the event.
Caress said there were no major injuries or "medical issues" on what was "a perfect day for a marathon with temperatures in the high 50s to low 60s."
Purcell also won the Buffalo Run half-marathon on Catalina and the Rose Bowl Half Marathon, making him the first to win all three races, Caress said.
Half the runners were women, he said.