Chase Kalisz won the first American medal of the Tokyo Games, taking gold Sunday in the men's 400-meter individual medley.
Jay Litherland made it a 1-2 finish for the powerhouse U.S. team, rallying on the freestyle leg to take the silver. Brendon Smith of Australia claimed the bronze.
Kalisz, a protege and former training partner of Olympic great Michael Phelps, touched first in 4 minutes, 9.42 seconds.
Litherland was next in 4:10.28, just ahead of Smith (4:10.38).
Kalisz flexed his muscles and then climbed atop the lane rope, splashing the water while a contingent of his teammates cheered him from the stands of the nearly empty Tokyo Aquatics Centre.
"U-S-A! U-S-A!" they chanted.
Litherland came over to give the winner a hug, having ensured the Americans got off to the best possible start at the pool.
The Americans seized their chance after Japanese star Daiya Seto stunningly failed to advance to the final, having finished ninth in the preliminaries after making a tactical error attempting to save his energy for the medal race.
The finals were held in the morning Tokyo time rather than their usual evening slot, a nod to U.S. television network NBC, which wanted to show the finals live in prime time back in America.
Team USA went on to win a record six of 12 medals available for the first night of swimming at the Olympics.