The Orioles had a few more players on provisional rosters who were not selected to play in the tourney. Second baseman Brian Roberts and closer George Sherrill didn't make Team USA's final roster, while reserve Oscar Salazar missed the final cut for Team Venezuela.
Guthrie learned of his selection last week and commented on the achievement.
"It's a great honor to have been considered and then selected," Guthrie said. "I'm very excited to wear USA across the chest, and to be surrounded by the type of players that will be on our team as well as the opposing teams."
Guthrie, Izturis and Mora are expected to leave the Orioles on Sunday to practice with their respective teams. Costanzo, who wasn't invited to Spring Training with the big league club, has already been practicing with Team Italy and played against Baltimore on Tuesday.
The tournament is not expected to impact any roster battles for Baltimore. Guthrie is entrenched as the ace, and Mora and Izturis all but have their starting jobs cemented.
Former Oriole Ramon Hernandez will do the catching for Venezuela, and two ex-players with Baltimore ties will be involved in prominent roles for Team USA.
Former Baltimore second baseman and manager Davey Johnson will manage the American national team, and former O's second baseman Bill Ripken will be his third-base coach.
The first round opens March 5 in Tokyo, with defending 2006 champion Japan facing China. Mexico City, Toronto and San Juan, Puerto Rico, host the other three first-round brackets, as follows:
Tokyo (March 5-9): Japan, China, Chinese Taipei, Korea.
Toronto (March 7-11): USA, Canada, Venzuela, Italy.
San Juan (March 7-11): Puerto Rico, Dominican Republic, Netherlands, Panama.
Mexico City (March 8-12): Mexico, Cuba, South Africa, Australia.
It's a double-elimination format this time in the first two rounds. The winners from Toronto will meet the winners from Puerto Rico in the second round at Miami's Dolphin Stadium, while the winners from Tokyo will meet with the winners from Mexico City in San Diego's PETCO Park. The semifinals and finals are on March 21 and 23 at Dodger Stadium.
Tickets are available through MLB.com, and MLB Network will televise 16 World Baseball Classic games, along with a nightly studio show dedicated to the tournament. ESPN will televise 23 games of the Classic in the U.S., including the semifinal and final games, across ESPN and ESPN2 and on its Spanish-language platform, ESPN Deportes.