Emily Sisson Runs Fastest Marathon by American Woman, Beats Record by 43 Seconds: 'Still Sinking In'

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Emily Sisson is on top of the world, and the record books.

The 30-year-old runner became the fastest American woman ever to run a marathon on Sunday, after finishing the Chicago Marathon with a time of 2:18:29.

Sisson, from Wisconsin, beat the previous record, held by Keira D'Amato, by an impressive 43 seconds, according to CNN. D'Amato set the record earlier this year at the Houston Marathon.

After the race, Sisson, D'Amato, and two other women who have held the record — Joan Benoit Samuelson and Deena Kastor — posed for a photograph that was shared on the Chicago Marathon's Twitter account.

"American record in the marathon today! 2:18:29. Still sinking in to be honest lol," Sisson wrote an Instagram post that showed her holding a sign that read, "American Record."

"So overwhelmed—in the best way—with all the kind messages and texts! Thanks everyone for all the support."

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Sisson told ABC affiliate WLS-TV that she didn't initially expect to break the record.

"I thought 2:20 was an ambitious goal, so to run 2:18:29 and finish second, I'm just ecstatic about it," she told the news station.

After D'Amato broke the marathon record earlier this year, she said she felt she wouldn't hold the title for long.

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"There's a number of American women that are also gunning for that record, so I think if I don't lower it myself, it's not going to be mine for very much longer," she said before the Berlin Marathon in September, per The New York Times.

While Sisson set the American record, she came in second during the women's race. First place went to Kenyan Ruth Chepngetich, who finished with a time of 2:14:18.

Kenyan runner Benson Kipruto won the men's title and finished at 2:04:24.

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Marathoner Marcel Hug finished the wheelchair race with a time of 1:25:20, setting an unofficial record, marathon officials said.

Per CNN, more than 40,000 people participated in the Chicago Marathon from 50 states and more than 100 countries.