The South Americans triumphed 25-23, 23-25, 25-18, 25-19 at the Isa Sports City Hall in Riffa in the Pool D encounter.

Poland are hoping to win a fourth title at the age group event but the third seeds will now have to do things the hard way.

Brazil, the fourth seeds, would be crowned as champions for the fifth time should they win the gold medal.

In the group's other match Italy beat Canada in straight sets, 25-17, 25-17, 25-15.

Pool B witnessed a shock as top seeds Cuba lost in four sets to South Korea.

The North American under-20 champions went down 27-25, 17-25, 25-22, 27-25.

Sixth seeds Argentina won the other match in the group against Egypt, 25-19, 26-24, 22-25, 25-18.

Record winners Russia began their tournament with a four-set victory over Czech Republic.

The 10-time champions are off and running in Pool C after their 25-22, 18-25, 25-21, 25-13 success which was a repeat of last year's European Under-20 Championship final.

Russia, the second seeds in Bahrain, also won that match in The Hague in The Netherlands.

In the other game in the pool fifth seeds and Asian under-20 champions Iran whitewashed Tunisia 25-13, 25-19, 25-19.

Pool A saw hosts Bahrain begin in fine style with a straight sets win over Puerto Rico.

The home side have targeted making the second phase and triumphed 25-18, 25-14, 25-20.

Seventh seeds China beat Morocco 25-16, 25-23, 25-13 in the pool's other match.

Action at the tournament will continue tomorrow.

The top two sides in each pool will qualify for Pools E and F, which will in turn offer two places each in the semi-finals.

The final will be held on July 27.