Caitlin Simmers won the World Surf League finals Friday, outdueling Olympic gold medalist Caroline Marks in the title match.

At 18, Simmers became the youngest surfer to win a world championship.

She eclipsed the record set by Carissa Moore, who was 18 years, 10 months and 18 days old when she won the Association of Surfing Professionals championship in 2011.

Simmers was 18 years, 10 months and 12 days old Friday when she triumphed at Lower Trestles in San Clemente, California.

Her victory over Marks, who won an Olympic gold medal less than six weeks ago and was looking for her second straight WSL finals victory, capped a spectacular season.

“I didn’t want Caroline to have it all because that girl wins everything and she’s like the hardest person to compete against,'' Simmers said during an interview on the WSL broadcast. "And she literally like never falls. So I was like, it is not going to be a walk through."

The Rookie of the Year in 2023, Simmers dominated 2024 while winning three of the nine events before the finals.

In the men’s side at the finals, American John John Florence won his third world title with a victory over Brazil’s Italo Ferreira.

Florence, 31, and Simmers each collected $200,000 for winning.

The women’s title match was a showdown between two top Americans and a tense best-of-three heats.

Simmers, the No. 1 seed, lost the opening heat to Marks, the No. 2 seed, who scored a 9.60 on a ride in the final seconds. But in the second heat, Simmers responded.

She posted rides of 9.20 and 9.17 for a staggering two-wave total of 18.37 out of 20.  It was the highest combined heat score in finals history, according to the WSL broadcast, and more than enough to win the heat from Marks, who had a two-wave score of 14.17.

Simmers prevailed in the third heat when she posted a two-wave score of 15.16 and Marks, who failed to find a suitable second wave, posted a score of 7.17.  

“It means so much,’’ Simmers sad. “I literally was like going through every single emotion today. And it’s just (expletive) crazy. I was feeling so much love today from everyone."

Marks, 22, won $100,000 as runner-up. The No. 2 seed, Marks defeated No. 5 seed Tatiana Weston-Webb of Brazil to reach the final match.

In a rematch of their gold medal match at the Paris Olympics, Marks caught the decisive wave with less than six minutes remaining to beat Weston-Webb, who won a silver medal in Paris.

Weston-Webb won $75,000 for her third-place finish. Rounding out the “final five,’’ Brisa Hennessey of Costa Rica finished fourth and won $60,000 and Molly Picklum of Australia finished fifth and won $40,000.

Follow Josh Peter on social media @joshlpeter11