Lee said the U-20 team will display a better performance in the knockout stage as they try to maintain a high level of concentration. The 19-year-old said South Korea still have more things to show at the tournament.

"We only showed 50 percent of our play," he said to reporters at Cheonan Football Centre, a training facility for the national team. "I think that's because our players felt the pressure to win, but I believe we will handle it and perform better tomorrow."

Lee, who has started all three South Korean matches so far as center back, said the players got a grip on Portugal's style of play after analyzing videos and having team meetings.

"Portugal attackers are good in penetrating opponent's defense," he said. "In our meeting, each of us said since one loss means elimination, we should give all-out efforts so that we don't have any regret left after the match."

Lee said communication between the players is important on the pitch and he is especially working closely with goalkeeper Song Bum-keun.

"Even if our attackers fail to score, we won't be losing if defenders don't concede a goal," he said. "If we can communicate closely, I think we can have a clean sheet."

From the round of 16, teams can enter a penalty shootout if the score is tied after regulation time and two 15-minute halves of extra time. Lee said the players are determined to finish the match in 90 minutes.

"We just have to execute what we have to do on the pitch," he said. "Portugal should be also adjusted to the environment here, but if we play with confidence, there won't be a big problem." (Yonhap)