YOKOHAMA, Japan — Behind one of its oldest and one of its youngest players, the United States toppled the Dominican Republic, 3-1, on Wednesday to advance to the semifinals and preserve its gold medal hopes.

Scott Kazmir, 37, who reached the major leagues this season after five years away, allowed just two hits over five scoreless innings while striking out five batters.

An All-Star with the Tampa Bay Rays in his early 20s, Kazmir made a comeback this major-league season, appearing in three games with the San Francisco Giants. When he was let go by the Giants, Team U.S.A. pounced, and the unemployed Kazmir seized the opportunity to pitch in the Olympics.

“I felt like I still had a lot in me, and I felt like the time off really did me well,” he said.

First baseman Triston Casas, 21, a top prospect for the Boston Red Sox, smashed a two-run home run in the first inning off Denyi Reyes, another player in the Red Sox farm system. It was Casas’s third home run of the Olympics. Designated hitter Tyler Austin added a solo blast in the fifth inning.

On Thursday, the United States will face the loser of Wednesday’s matchup between South Korea and unbeaten Japan. Another win, and the United States will play for its first gold medal in baseball since 2000.

Despite the loss, the Dominican Republic advanced to the bronze medal game, where it could claim its first Olympic medal in baseball.