The Americans remain in the competition but the preliminary round setback -- only their third loss in 112 Olympic matches spanning 72 years -- is a huge embarrassment to the inheritors of the Dream Team tag.
When NBA professionals were allowed to compete in the Olympics for the first time in 1992, some of the greatest players in the game's history responded by forming up for an unprecedented alliance.
Michael Jordan, Magic Johnson, Larry Bird, Charles Barkley, Patrick Ewing and Karl Malone were among a superpower squad that became one of the focal points for the Barcelona Games and even the most idealistic defender of the old Olympic amateur ideal could hardly deny them the Dream Team title.
Four years earlier a team made up of American college players had been beaten by the Soviet Union in the semi-final rematch of their infamous 1972 encounter when the USSR controversially, on the buzzer, ended the Americans' 64-game Olympic winning streak that had earned seven consecutive golds.
The 1992 Dream Team duly steamrollered everyone in their path, part embracing the Olympic ideal and part ignoring it as the giant millionaires opted to stay in top hotels instead of the athletes' village at Barcelona.
Four years later, on home soil in Atlanta, they again cruised to gold with another team containing the cream of the NBA. Though Jordan had gone, Shaquille O'Neal had arrived and the basketball proved one of the biggest draws of the Games.
SYDNEY WARNING
By Sydney 2000, the novelty was beginning to wane and the Dream Team tag was wearing thin.
It also looked entirely unsuitable as, in what now looks something of a warning for Sunday's shock, the United States came desperately close to losing to Lithuania in the semi-final.
They avoided humiliation by a whisker and went on to beat France comfortably in the final.
Four years on, a dozen of the NBA's best players declined to make the trip to Athens and though the young team still looked formidable on paper they appeared vulnerable on a six-game European warm-up tour.
Those fears proved well-founded when Puerto Rico, who had lost five times to the Americans in the last 13 months, not only beat them but blew them away.
Puerto Rico, from the U.S. territory of four million, were in no way overawed by their big brother neighbours; storming into a 22-point halftime lead they stayed comfortably clear throughout as a U.S. comeback failed to materialise.
The result does not end the U.S.'s chances -- four teams from the pool of six will qualify for the quarter-finals -- but it has certainly removed any lingering concept of invincibility and final consigned to Dream Team epithet to Olympic history.
