WARSAW, June 9 (Xinhua) -- All four places in the semifinals have now been booked at the ongoing Under-20 World Cup in Poland after Ecuador and South Korea beat their respective opponents on Saturday.

In a thrilling encounter, Ecuador gave the United States their marching orders after a 2-1 win at the Gdynia Stadium. "We're so proud of our boys," the Ecuadorian president gushed on Twitter. "Terrific mentality and togetherness. That's the Ecuador that's emerging. Let's stride into the future together!"

In a brief statement, the Ecuador coach Jorge Celico told the media that his team had "developed brilliantly here in Poland. We were lacking a bit of self-confidence at the start, but that's grown with each passing game."

As for the U.S., coach Tab Ramos lamented the disappointing result, but said the team had "shown we can compete with the best teams in the world. That's a great accomplishment for us."

In the other big encounter, the South Korea and Senegal slogged out a hard fought 3-3 battle, with a South Korean triumph after a 3-2 penalty shoot-out.

On Friday, Ukraine edged Colombia 1-0 and Italy saw off Mali 4-2 in the quarterfinals.

The semifinals will take place on June 11, with Ukraine taking on Italy in Gdynia, and Ecuador facing South Korea in Lublin.