Home runs from first baseman Tristan Casas and shortstop Nick Allen lifted the United States baseball team to a 4-2 win over South Korea in a pool play matchup.
The U.S. improved to 2-0 in the Olympic tournament, advancing as one of the top two seeds to the modified double-elimination knockout round.
Casas, 21, and Allen, 22, are among the youngest members of the American squad which includes a wide range of MLB veterans and prospects.
Both players are considered top prospects for their MLB clubs. According to MLB.com, Casas is rated as the Boston Red Sox's No. 1 prospect while Allen is ranked third in the Oakland Athletics' system.
Following an 8-1 opening game win against Israel, the U.S. faced a much stiffer test in the form of South Korea, the defending gold medalists from Beijing 2008, the last Olympics to include baseball.
South Korea got on the board first, as U.S. starting pitcher Nick Martinez allowed singles to the game's first two batters. A no-out fielder's choice brought Korean leadoff hitter Park Hae-Min home from third, though Martinez escaped further damage to keep the Korean lead to 1-0.
Martinez then found his groove, retiring 12 of the last 14 batters he faced and striking out nine. He was replaced after five innings of one-run ball.
Casas gave the U.S. an instant 2-1 lead in the fourth inning with his long ball, which also scored second baseman — and American flagbearer from the Opening Ceremony — Eddy Alvarez.
Allen followed one inning later with a solo shot, followed swiftly by a Tyler Austin RBI single to put the U.S. up 4-1.
Closer David Robertson worked into some trouble in the ninth and allowed South Korea's second run but ultimately pitched out of the jam to seal the win.
With a perfect 2-0 record in an abbreviated pool round, the American earned a BYE into the second round of the knockout stage. There, they will take on the winners of the opposite three-team pool, host nation Japan. The winner of that matchup will advance directly to the semifinals, while the loser will have the opportunity to work their way back into the medal hunt but will have to go through the loser's bracket.