It is a third title in a row for the US, for whom Jake Williams (26 points) and Steve Serio (24) dominated the scoring.
Lee Manning (21), Pratt (17) and Gregg Warburton (15) kept Britain in the game until the final minute.
“They are a hell of a team and Steve Serio was incredible – he’s one of the greatest to ever play the game. We challenged him to shoot and he came out firing,” said Pratt.
“We stuck to our gameplan but they were the better team.”
Terry Bywater, competing at his eighth Games, having made his debut as a 17-year-old in Sydney 2000, added: “We had such a fantastic tournament. The boys stuck together, but getting beaten by four points in a final, it’s going to hurt.
“They made some big shots down the stretch. They have a lot of experience in these finals and it’s the first time we’ve been there in many years. I’m so proud of the boys.”
Earlier on Saturday, the GB women’s team beat Germany 48-39 to finish fifth in their competition.