For Katie Ledecky, Olympics open with a complicated loss to her biggest rival

Australia’s Ariarne Titmus, center, celebrates her gold medal in the women’s 400m freestyle, joined by silver medallist Summer Mcintosh of Canada and bronze medallist Katie Ledecky of the United States, Saturday at La Defense Arena during the 2024 Summer Olympics in Paris. (Chang W. Lee/The New York Times)

NANTERRE, France — Ariarne Titmus got to her lane first. Or so she thought.