THESSALONIKI, Greece -- Oklahoma freshman De'Angelo Alexander scored 13 points to lead the unbeaten United States over Nigeria 88-68 Saturday at the World Junior Basketball Championship.

The Nigerians trailed by only two points late in the first half, but the American defense eventually shut them down.

The U.S. team improved to 3-0 and advanced to the top group in the second round, which begins Monday. Nigeria (1-2) will play in the lower group in the 16-team field.

In other games, Sasa Zagorac scored 23 points as Slovenia (2-1) beat China 87-78, Lithuania (2-1) defeated Venezuela 108-60 behind Martynas Mazeika's 28 points, and Puerto Rico (2-1) got past Angola 85-71 with 28 points from Jose Barea.

Also, Croatia (3-0) beat Malaysia 110-65, and Australia (3-0) also advanced to the top group by defeating Korea 124-95.