It was billed as one of the most anticipated races of the Paris Olympics.

Ariarne Titmus turned it into a blowout.

Titmus left Katie Ledecky in her wake on a raucous opening night at La Defense Arena, leading from start to finish to win the 400m freestyle on Saturday.

Titmus, the Australian star known as “Terminator,” handed Ledecky a second straight Olympic defeat in an event the American won at Rio de Janeiro in 2016.

With her fingernails painted Aussie yellow, Titmus strolled on deck with the confidence of a reigning champion, flashing a big smile and waving to the fans.

Titmus actually faced her stiffest challenge from Canadian 17-year-old phenom Summer McIntosh, but won comfortably in 3 minutes, 57.49 seconds. McIntosh claimed the silver in 3:58.37. Ledecky wasn’t even close, settling for bronze in 4:00.86.

“My legs are a bit tired, but I’m just relieved more than anything,” Titmus said. “I probably felt the expectation and pressure for this race more than anything in my life, to be honest, and I’m pretty good at handling the pressure of it.”

Ledecky, 27, remains at six individual gold medals in her brilliant career, still the most by any female swimmer in Olympic history. But, she couldn’t find the speed to chase down Titmus. “I just didn’t have it on the last 200 or 250 that way I wanted to,” Ledecky said.

Ledecky posted the fastest qualifying time in the morning heats, but Titmus was clearly saving herself for the race that mattered most. She went nearly 5 seconds faster in the evening.

Aussies vs Americans

Australia also won the gold in the women’s 4x100m freestyle relay, claiming their fourth straight Olympic title in the event. The quartet of Mollie O’Callaghan, Shayna Jack, Emma McKeon and Meg Harris set an Olympic record with a winning time of 3 minutes, 28.92 seconds.

The Americans — Kate Douglass, Gretchen Walsh, Torri Huske and Simone Manuel — rallied to take silver. China took bronze.

The Americans finally had something to cheer about when when Caeleb Dressel anchored the men’s team to victory in the 4x100m freestyle relay.

It was the eighth medal of Dressel’s career — all of them gold. He won five of those at the Tokyo Games, and he could be setting up for another glittering haul in the City of Lights.

On deck after the medal ceremony, Dressel embraced his 5-month-old son, August, with tears streaming down his face. It was an especially satisfying moment for a generational swimmer who fell out of love with his sport after Tokyo, leading him to take an extended break.

“It takes me back to my first gold,” the 27-year-old Dressel said. “It really doesn’t get old.”

Australia, anchored by Kyle Chalmers, took the silver in 3:10.35, while the bronze went to Italy in 3:10.70.

Germany’s Lukas Märtens won the first swimming gold of these Games, knocking off three world champions in the men’s 400m freestyle.

Märtens set a blistering pace through the first 300 meters and held on at the end to touch in 3:41.78.