Coburn is the first American, male or female, to win gold at a global championship since Horace Ashenfelter won the Olympics in 1952.
The 26-year-old's winning time of 9:02.58 shaved five seconds off her own American record, which she had set en route to earning bronze at the Rio Games. The time stands as the new World Championships record.
Frerichs, who was 11th in Rio, ran 9:03.77, a new personal best by 16 seconds. Coburn and Frerichs' marks make them the sixth and seventh-fastest performers in world history.
Things got off to a weird start when Beatrice Chepkoech of Kenya, one of the medal favorites here after winning the Paris Diamond League, nearly missed the first water jump.
She ran at the front of the pack and instead of cutting to the inside of the track to approach the water jump, she kept running on the curve, even as the rest of the pack cut in. The 26-year-old turned back and got over the water jump, then appeared to fall while jumping over the next barrier.
She returned to the lead group within the next 200 meters, which was by now led by world record holder and Olympic champion Ruth Jebet of Bahrain, who started to ratchet up the pace just after 1K with defending world champion Hyvin Jepkemoi of Kenya, 18-year-old world junior record holder Celliphine Chespol of Kenya and Americans Coburn and Frerichs in tow.
On the second-to-last water jump, Chespol fell off the pack and was nowhere to be seen at the bell lap, where Jebet started to falter and Frerichs moved up on the outside to the lead.
On the backstretch, Frerichs ran on the outside, stride-for-stride with Jepkemoi, while Chepkoech and Coburn were in close pursuit. Coburn went over the final barrier on the inside and took the advantage when the runners hit the closing straight. She would finish in 9:02.58 to break her own American record by five seconds.
EMOTIONS!!!! pic.twitter.com/R9EuzJEr8E— FloTrack (@FloTrack) August 11, 2017
Coburn's decision to switch coaches from Mark Wetmore, her longtime mentor at the University of Colorado, to her fiancé, Joe Bosshard, a year after earning Olympic bronze appears to have paid dividends, though her training partner in Aisha Praught of Jamaica was disqualified.
"The last two years at the Olympics and World Championships in 2015, my last water jump wasn't very powerful and so that was something I really needed to work on," Coburn said after her victory lap to Lewis Johnson of NBC. "My fiancé and coach Joe said 'be really powerful that last water jump' and that's really what I was thinking, to hang on for that last water jump."
Watch Emma Coburn's sister, Gracie Willette, react to Emma winning gold:
"My coach told me 'just go for it,'" Frerichs said of going for the lead on the bell lap. "He told me Emma races smart and I felt very comfortable following her, her form is great and there was an extreme level of comfort."
Frerichs was racing not only for herself but also Bowerman Track Club teammate Colleen Quigley, who was disqualified from the preliminary round for twice stepping on the white line designating the track from the infield immediately following the water barrier. With a full team, could the United States have swept all three medals today?
Is it possible to cry happy and sad tears at the same time? So many mixed emotions tonight watching the steeple final from the stands...— Colleen Quigley (@steeple_squigs) August 11, 2017
Final results below: