American teenager Regan Smith made a huge splash in the pool Friday morning when she broke Missy Franklin’s world record in the women’s 200-meter backstroke at the world swimming championships.

The 17-year-old won her semifinal heat in 2 minutes, 3.35 seconds, putting her ahead of the mark of 2:04.06 set at the 2012 London Olympics by Franklin, the most decorated female swimmer in the history of the world championships.

“I’m in shock,” Smith said. “I really don’t believe it.”

MICHAEL PHELP'S 10-YEAR WORLD RECORD IN 200 BUTTERFLY BROKEN BY HUNGARIAN TEENAGER

Franklin was also 17 in 2012 and won the gold medal in the event en route to her four gold medals that summer.

“Well dear friend, we had a great run. Seven years and I couldn’t be more honored to have my 200 back World Record broken by @reganesmith4, one of the sweetest and hardest working athletes I’ve ever known. Keeping this World Record with an American flag by it means everything,” Franklin, who retired last year, tweeted in a series of messages Friday.

“I was truly blown away watching Regan swim 2:03.3 (yes, I typed that right) and absolutely smash it. I’ve said it before, and I’ll say it again. People will forget our times, they’ll forget the color of your medals, but they will never, ever forget how you made them feel,” she continued. “I truly couldn’t be happier seeing my World Record go to someone who I believe at the bottom of my heart is one of the greatest inspirations and kindest humans in the world. Congrats my dear @reganesmith4. Thank you. For sharing your gift with us. You’re beyond a joy to watch.”

Smith’s heat was 3.22 seconds faster than Canadian Kylie Masse, who was the second-fast qualifier. Their final is set for Saturday night in South Korea.

FLASHBACK: FIVE-TIME OLYMPIC CHAMPION MISSY FRANKLIN RETIRES FROM SWIMMING AT AGE 23

Another American also broke a world record on Friday, when Caeleb Dressel beat Michael Phelps’ record in the 100 butterfly.

Dressel won his heat in 49.50 seconds – 0.32 seconds faster than Phelps’ mark set at the 2009 world meet in Rome at the height of the high-tech suit era.

“Just the standard that Michael set, wanted to go after it,” Dressel told reporters after the heat. “I hope he was happy watching me do that.”

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Meanwhile, fellow American Simone Manuel won her second straight title in women’s 100 free at the world championships.

Relegated to Lane 1 with the slowest qualifying time, the 22-year-old Texan led all the way and touched first in 52.04 seconds, beating Cate Campbell of Australia by 0.39 seconds.

“Not everyone has a perfect swim every time so I just needed to regroup and put on a good face,” Manuel, who did not have the best 100 freestyle qualifier by her standards. “I’m a veteran on the team, so I have to be able to show a little bit of poise in these hard moments.

Sarah Sjostrom of Sweden, the world-record holder, took bronze.

The Associated Press contributed to this report.