The Czech Republic began the tournament with a big win ©Twitter/WBSC

The Czech Republic stunned the host nation in what was not the only upset of the opening day of the Under-23 Baseball World Cup in Sonora in Mexico.

A four-run third inning, capped by Marek Chlup driving home three runs with a bases-loaded double, got Czech noses in front and they would not let the led slip.

Pitcher Ondřej Satoria also impressed, striking out five batters and allowing only one run in 5.2 innings of work.

Chinese Taipei were the other Group A team to win on day one at the Estadio Yaquis, defeating Germany 7-0.

Cuba's game with the Dominican Republic was rained off.

In Group B, top-ranked South Korea dropped their opening game, losing 6-4 versus Nicaragua.

Luis Montealto had a monster game, driving in five runs in the last two innings as Nicaragua rallied from 3-1 down to triumph. 

Venezuela beat The Netherlands 9-4 and Colombia swept aside Panama 7-1 in the group's other game at the Estadio Sonora.

The top three finishers from each group will advance to the super round, which is set to be played from September 29 to October 1.

This is the first Baseball World Cup staged by the World Baseball Softball Confederation since 2019, and had been due to take place last year before being delayed because of the coronavirus pandemic.