For more than a decade, Katie Ledecky has dominated the pool like no other woman.

She piled up world records and gold medals, usually with jaw-dropping margins of victory that made her appear to be swimming a different race than the competitors fighting for second place.

But Ledecky’s invincibility vanished Monday against Australian sensation Ariarne Titmus in front of a few hundred athletes, coaches, journalists, and officials at the cavernous Tokyo Aquatics Centre.

Titmus, nicknamed “The Terminator,” blew past Ledecky in the final stretch of the 400-meter freestyle to win gold in the most anticipated swimming final at these Olympic Games.

“It’s the biggest thing you can pull off in your sporting career, so I’m over the moon,” the 20-year-old Titmus said. “I’m trying to contain it as much as I can.”