Puerto Rico, who finished as the runner-up in the 2013 edition of the tournament, join Japan and The Netherlands among the four nations competing in Los Angeles next week. 

The Puerto Ricans started sublimely, scoring four unanswered runs in the first innings.

The Americans cut the deficit with a single in the second, but neither side failed to add any further runs until the hosts added another single in the fifth to take the score to 4-2.

Puerto Rico added two more in the sixth while another American single kept them just in contention at 6-3.

Two more runs were scored by the US in the ninth, but they were unable to add a third to draw level which saw the Puerto Ricans claim a 6-5 victory.

"This is an unbelievable win for us," said Puerto Rico's Carlos Beltran.

"The fact that we get the opportunity to go to the finals in LA really means a lot to us.

"So we're happy, and I know our people in Puerto Rico are very happy also."

The US can still the reach the last four. 

However, today's result eliminated Venezuela, who have failed to win either of their matches in the second round so far. 

Action in Pool F is due to resume this evening when Venezuela meet Puerto Rico in what is a inconsequential fixture.

The line-up for the last four will then be confirmed when the US take on the Dominican Republic tomorrow, with the winner of that contest progressing to the final four.

The semi-finals are due to take place on March 20 and 21 before the final brings the competition to a close on March 22.

Japan and The Netherlands have already secured their places in the last four after they finished top and second of Pool E respectively.

All three of the final matches are set to take place at the Dodger Stadium in Los Angeles.