By TIM REYNOLDS LAS VEGAS (AP) — This is not how USA Basketball expected to open its Olympic summer. Nigeria probably didn’t expect it, either. If there was any expectation of invincibility for the Americans heading into the Tokyo Olympics, it’s already gone — after Nigeria beat the U.S. 90-87 on Saturday night, an international shocker pulled off by a roster primarily filled by little-known NBA players that found a way to beat a group of All-NBA, All-Star and max-contract performers. “We just wanted to compete,” said Nigeria’s Gabe Nnamdi, who goes by Gabe Vincent when playing for the Miami Heat. “We know what USA Basketball means around the world and what they’ve stood for for so long.” Nigeria'