It started with a 'boom' from an artillery piece. In seconds, the first of 30,000 runners, legs churning, arms pumping, were on their way.
"Once the gun goes, they're on autopilot," grinned Rick Nealis, race director of the Marine Corps Marathon.
In preparing for this year's race, an event that started in 1976, organizers and runners cast a wary eye on the skies, watching for signs of Hurricane Sandy.
"I've been through hurricanes," says runner Zack Stock. "I've lived in Texas for three years. It's going to be nothing."
Nevertheless, race coordinators felt they had to be prepared.
The biggest worry wasn't rain - there have been several wet marathons through the years - but high winds.
"Rain, we are going. Rain is fine," Nealis says. "Wind was always going to be a concern."
Timing, and geography were crucial.
For many runners, the race is not just an athletic event, but also a social gathering that can go on all day.
Dozens of temporary structures, including tents, grandstands, and checkpoints, need to be disassembled and moved away.
"If there's damage starting to happen, or we lost electricity, I start to lose some of the safety and security elements of the race," Nealis says.
But as runners made their way through the 26.2-mile course, the day unfolded as cloudy, overcast, and windy. But with no major signs of Sandy.
"I wasn't even thinking about it, so I just kind of went through it," says runner Teig Choroszy, who dedicated her race to her boyfriend in Afghanistan.
"My mom is flying back to Maine on Monday, and even this morning she goes 'oh honey, the airline's calling.' I'm like, mom, we're running a marathon, don't worry about it," she adds.
It was an extraordinary day for Augustus Maiyo, who's been training in Colorado for several years now.
"This is my first marathon. I've never run it before," he says.
That didn't stop the Kenya native from winning the race in two hours and thirty minutes. He too, was keeping an eye on conditions.
"The weather is good, but the wind is really bad," Maiyo says. "Twenty miles an hour down the river."
Women's winner Hirut Guangul, from Ethiopia, finished just fourteen minutes later.
Both runners say they were relieved the storm didn't interfere with the race.
"I didn't think about where I was. Only think running," Guangul says.
Choroszy, who ran the race in two hours and forty-seven minutes, says she was hoping for a faster time, but adds, she was proud to take part in this event.
"I gave it my all and I finished, and I have no regrets, and I'm glad I could take part in this," she said with a smile.