Yannick Agnel, the Olympic champion, led at 50.64 after 100 with Ryan Lochte in third. Agnel was up by nearly 1.5 seconds at 150 with Danila Izotov and Lochte in line for second and third.
But Conor Dwyer came from behind to surprisingly keep Lochte, the defending world champ, from medaling.
Agnel is coached by Michael Phelps‘ former coach, Bob Bowman.
Dwyer, 24, wins the first individual major international medal of his career.
Lochte, who wore lime green sneakers in his walk out to the deck, is scheduled for five more events in Barcelona. He swims in the 200 individual medley prelims Wednesday morning and semifinals Wednesday evening.
“I just tried to hit my last turn,” Dwyer told Universal Sports. “Michael (Phelps?) was texting me yesterday, ‘Stop taking it out like a little girl.”
Gold: Yannick Agnel (FRA) 1:44.20
Silver: Conor Dwyer (USA) 1:45.32
Bronze: Danila Izotov (RUS) 1:45.59
4. Ryan Lochte (USA) 1:45.64
5. Kosuke Hagino (JPN) 1:45.94
6. Robbie Renwick (GBR) 1:46.52
7. Cameron McEvoy (AUS) 1:46.63
8. Thomas Fraser-Holmes (AUS) 1:47.11
NBC Sports will air coverage of 87 Alpine skiing races at 22 resorts across the globe this fall and winter, from October through March, in the final full season before the 2018 Olympics.
Highlights include fall and winter stops in the U.S. with races in Killington, Vt.; Beaver Creek, Colo.; Squaw Valley, Calif.; and the World Cup Finals in Aspen, Colo., in March.
Lindsey Vonn‘s highlighted World Cup stop will be downhill and super-G races in Lake Louise, Canada, the first weekend of December.
The world championships in February will be in St. Moritz, Switzerland, where Ted Ligety and Mikaela Shiffrin will look to defend titles.
ALPINE SKIING SEASON PREVIEWS: Men | Women
Canadian skier Phil Brown was fortunate to walk away from an airborne crash at the World Cup season opener in Soelden, Austria, on Sunday.
Brown failed to finish his first run, losing contact with the snow early on and falling hard onto his side.
He tweeted a video of the crash, with slow-motion replays, with a soundtrack of Irish singer Enya‘s “Only Time.”
The World Cup season continues with men’s and women’s slaloms in Levi, Finland, in three weeks.
MORE: Ted Ligety recovers to finish fifth in first race in 9 months