YOKOHAMA—The United States beat South Korea 4–2 to earn a day off before the Tokyo Games baseball quarter-finals, just as Japan did in a 7–4 win over Mexico earlier on Saturday. Both teams now move to double-elimination play. South Korea take on the Dominican Republic on Sunday, while the United States face Japan on Monday. Triston Casas, a prospect for Major League Baseball’s Boston Red Sox, belted a two-run homer in the fourth inning for a 2–1 U.S. lead. In the next inning, shortstop Nick Allen’s solo shot and a trio of singles made it 4–1. U.S. starting pitcher Nick Martinez, who allowed a run and struck out nine, said watching Korean league games while stuck at a home during COVID-19 lockdowns led to his good performance. Neither side recorded a hit in innings six through eight. In the ninth, U.S. closer David Robertson let in a run on a …