Officials exploded a backpack found inside the Olympic basketball arena while Spain and Nigeria started their men's game in the nearly entirely empty building.
A statement from the Rio Olympic Committee said the backpack was found near a trash container in the bathroom on the top floor. Ticket holders were prevented from entering Carioca Arena 1 because the bag was next to a spectator passageway.
The controlled explosion under the guidance of the Federal Police and the Army reverberated with a boom that jarred Spain center Pau Gasol as he was about to take the court.
"We thought, I guess nobody came to watch the game," Gasol said. "We heard an explosion but we didn't know exactly what it was or how big it was. We thought it was fireworks or, I don't know. The arena was pretty much dead empty at the beginning.'"
Officials say the backpack contained a tablet, a pair of socks and a jacket.
Inspectors allowed the game to start on time, and for volunteers and the media to remain in the building. Spectators were allowed to enter in the first quarter.