Olympic bronze medallist Maurice Greene anchored the United States team to an easy victory in the first-round heats of the 4x100 metres relay on Friday.
"Tomorrow we will strike it out and let the times drop," said Greene, who predicted the U.S. would break the world record of 37.40 seconds they set at the 1992 Barcelona Games.
"It was easy, it was fun," he added after the defending champions clocked 38.02 in heat two. Britain were second in 38.53.
Olympic 200 metres champion Shawn Crawford ran the first leg for the Americans, handing over to Darvis Patton who in turn passed the baton to Coby Miller. The United States rested Olympic 100 metres gold medallist Justin Gatlin.
Crawford said he had not known until Friday morning that he would be required to run in the first round.
"I just want to help my team win," he said. "I'm only tired when I'm done."
Nigeria won the first heat in 38.27. The final is on Saturday.
Olympic women's 400 metres hurdles gold medallist Fani Halkia was again given a rapturous reception when she ran the final leg for Greece in the 4x400 relay heats.
Halkia streaked around the track to move Greece to second place behind the United States in heat two. Russia won the first heat.
Britain and the United States respectively won the two first-round heats in the men's 4x400 relay.
