"It was a difficult match physically," U.S. coach Steve Swanson said. "Nigeria gave us all we could handle and a little more. Getting that first goal was key for us." The Americans, who won the tournament in 2002 and 2008, will face either Japan or defending champion Germany in Saturday's final. The second semifinal was set to be played later Tuesday.
Brian opened the scoring with a header in the 22nd minute and Ohai doubled the lead in the 70th, taking a through ball from Samantha Mewis and beating Nigeria's goalkeeper Ibubeleye Whyte with a right-foot shot from 12 yards.
Nigeria pressed forward after the second goal, but the Americans denied them a chance to get back in the game.
"I thought our back four did a very good job of keeping possession and allowing us to get out of our end," Swanson said.