The increasingly clandestine South Korea trained behind closed doors for the third straight day on Sunday, with the ever-important opening group match against Russia just round the corner.

South Korea on Sunday arrived in Cuiaba, the site of its Group H contest against Russia two days later. The Asian representative trained at the Federal University of Mato Grosso in the central-west city, and head coach Hong Myung-bo opened only the first 15 minutes of the session to the media.

The match between the 57th-ranked South Korea and the 19th-ranked Russia will kick off at 6 p.m. Tuesday at Arena Pantanal in Cuiaba, in the central-west region of Brazil. It will start at 7 a.m. Wednesday (South Korean time).

South Korea, competing in its eighth straight World Cup, will later take on Algeria and Belgium.

Hong also showed the opening 15 minutes of the team's practice two days earlier at its base camp in Foz do Iguacu, about 1,100 kilometers south of Cuiaba, and then kept the entire practice off limits on Saturday. With little on display in the opening 15 minutes -- other than the sight of players stretching -- South Korea has essentially slammed the doors shut for three consecutive days. An official with the Korea Football Association (KFA) said Hong plans to keep upcoming practices equally secretive.

Hong has frequently talked about the importance of shoring up the defense. A pair of open sessions earlier in the week provided a glimpse into the coach's commitment, as the players went through rigorous drills aimed at improving their positioning and forechecking.

After the practice, forward Lee Keun-ho said it will take a team effort to play good defense.

"We have to be physical as we have practiced all along, and we have to help each other out," he said. "I think we have to go the extra distance. I've been watching some (World Cup) games on television, and I think players have had a tough time dealing with humid conditions in some places. We all have to bear down and concentrate harder during crunch time."

Lee, ahead of his first World Cup, said he is getting some butterflies in his stomach as the start of South Korea's campaign nears, but also said being a bit nervous has actually helped him prepare with more focus and intensity.

With so much emphasis being placed on defense, it may be easy to forget about South Korea's offense -- or lack thereof.

Having scored only 15 times in 16 matches under coach Hong, South Korea will need to address its scoring woes or it will be in for a short tournament.

Striker Park Chu-young, who leads the squad with 24 goals in 64 matches, will be under pressure to lead the attack. He said Sunday he has put aside all personal ambitions.

"The most important thing is for the team to win," he said. "Whether it's helping out on defense or trying to score goals, I will do everything I can to help us win."

Park is one of five carryovers from the previous World Cup in South Africa. Another attacking player, winger Son Heung-min, will be playing in his first World Cup, but if the 21-year-old is nervous, he isn't showing it.

"I know the World Cup is a challenging event," the Bayer Leverkusen youngster said. "But I am trying to stay as cool and collected as I can. I am sure Russia has been preparing hard for this, too."

Earlier on Sunday, FIFA announced that Nestor Pitana of Argentina will be the referee of the South Korea-Russia match. He refereed the final of the 2013 Copa Libertadores, a prestigious club competition held annually in South America. Pitana will turn 39 on the match day, FIFA added.

Two more officials from Argentina, Hernan Maidana and Juan Pablo Belatti, will serve as assistant referees. Roberto Moreno of Panama will be the fourth official and Eric Boria of the United States will be a reserve assistant referee, according to FIFA. (Yonhap)