From left, Nicole DiMercurio, Rachel Hyland and Sarah Sellers approach the 24-mile marker of the Boston Marathon on Monday. (Scott Eisen/Getty Images)

Many who watched the Boston Marathon — even those who follow the sport of running — had the same question Monday: Who in the world is Sarah Sellers?

Sellers crossed the finish line in second place at the prestigious 26.2-mile race in rain-soaked conditions as a virtual unknown. Few online road-race results existed for Sellers, and she was not listed among the elite field. In the wet and windy conditions, Sellers wore a nondescript outfit, with no visible sponsors, and simply clicked the timer on her watch after crossing the finish line.

Her time of 2 hours 44 minutes 4 seconds left her in second place, and she was among seven American women in the top 10. Desiree Linden was the first American woman to win the race since 1985, a historic finish in a race full of surprises. But Sellers’s finish might have been the most improbable.

“I mean, I still can’t believe I finished second,” Sellers, 26, said in a phone interview Monday afternoon. “I’m going to wake up and this will be a dream.”

Sellers (née: Callister) never planned to podium at Boston. Not when she was a standout runner at Weber State University in Ogden, Utah, where she grew up. Not even when she qualified for Boston after winning the Huntsville (Utah) Marathon in September in 2:44:27.

She only signed up for Boston because her younger brother, 25-year-old Ryan Callister, was running it. (He finished in 2:48:20.) Plus, she’s a nurse anesthetist who works full-time in Tucson. She doesn’t have an agent, or any sponsors, and has to fit in her workouts at either 4 a.m. before work or 7 p.m. after her 10-hour shifts at Banner Health Center.

Over the past few months, Sellers mainly trained by herself, running six days a week and up to 100 miles.

Sellers may have been “one of the most sought-after prep runners in the state of Utah,” as her college bio states, but she was essentially an anonymous runner competing against the biggest names in the sport Monday.

When a race official told Sellers she finished second, she figured that meant in her age group. Sellers views the professional runners she beat as idols, not peers — “not only the American women, but also the international field,” she said.

“Obviously the conditions were the wild card that everyone got dealt, but I think it played to my advantage,” Sellers said. “Looking at my time going into the race, I shouldn’t be on the same page as any of the top 20 women. … They’re in a different league than me.”

But for one day, Sellers could say she was among the best. She earned $75,000 for her second-place finish, which she said would go toward paying off her and her husband’s student loans.

“I honestly didn’t think I would have anything to celebrate,” Sellers said.

Her coach, Weber State’s Paul Pilkington, told her to go out conservatively, and for the majority of the race, Sellers hung back. When the fourth-place woman, Rachel Hyland, made a move around Mile 20, Sellers followed.

As others started to fade, Sellers said she felt strong in the final stretch. She ran her second 13.1 miles faster than her first.

“I think the biggest thing is her mental toughness,” Pilkington said. “She’s a little bit taller, so you’d think the wind would be detrimental, but she’s really strong.”

Sellers wants to qualify for the “A” standard for the 2020 Olympic marathon trials (2:37:00) and said her Boston performance gives her confidence. She has no plans to scale back on her nursing job — “It’s really rewarding and gives me perspective on life,” she said — and intends to run another marathon this fall.

To celebrate, she said she’ll treat herself to a few leisurely activities she didn’t have time for before Boston, like mountain biking and running on trails. On Wednesday, she will return to work a nursing shift, living a life similar to the one she did before.

Except now, fewer people will have to wonder who Sarah Sellers is.

Correction: An earlier version of this article misstated the age of Ryan Callister. He is 25, not 24.

More on the Boston Marathon:

Desiree Linden becomes first American woman since 1985 to win the Boston Marathon

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