Bulgaria and Nigeria confirmed their spots in the last-16 of the International Volleyball Federation Boys' Under-19 World Championship as the pool phase concluded in Tunis.
The Bulgarians scored a tournament high 18 blocks as they defeated Colombia 25-16, 25-21, 24-26, 26-24 in Pool B at the Salle Polyvalente Radès.
They needed two match balls to take the win against the tournament debutants before Georgi Tatarov scored with an ace to seal victory.
Italy topped the group with a 25-16, 25-18, 24-26, 25-11 win against defending champions Iran, with both teams having already sealed their places in the knock-out round.
In Pool D Nigeria needed only a set in their final pool match to secure their last-16 spot.
They took all three in a 25-17, 30-28, 25-17 win as they eased to victory against the Dominican Republic.
Russia remained unbeaten at the top of the pool with a 25-12, 25-19, 25-12 win against the United States.
Belarus stunned Cuba 25-21, 25-23, 22-25, 25-16 in Pool A, allowing Brazil to overhaul the Central Americans at the top of the pool with a 25-17, 25-17, 25-20 triumph against Chinese Taipei.
Japan fell to a 23-25, 25-18, 24-26, 21-25 loss to Argentina in Pool C as Germany secured their second win of the tournament in a 25-21, 23-25, 25-18, 14-25, 15-12 win against Mexico.
The tournament resumes with the knock-out phase on Tuesday (August 27).
Tunisia, Colombia, Mexico and the Dominican Republic, who all ranked fifth in their pools, will play a round-robin pool to confirm 17th to 20th positions.