The 25-year-old swam a scintillating breaststroke leg to take charge, touching in 4:32.08s ahead of US pair Emma Weyant (4:32.76s) and Hali Flickinger (4:34.90s).

“I swam, believing in myself. I really did not think of winning the gold,” said Ohashi.

“A lot of people supported me so that I could exert all my strength. I really appreciate it. I had an enjoyable race. It is still like a dream.”

Hungary’s Hosszu, a dominant force since setting the world record at the Rio Olympics in 2016, was in touch over the first 200m but the world champion failed to deliver the killer punch she so often has before.

Flickinger set the early pace, turning first after the butterfly leg with Hosszu second, and the American maintained her lead through the backstroke.

But Ohashi pulled a body-length clear in the breaststroke and no one could rein her in, with the battle unfolding for the minor medals.