Due to Tiger pitching injuries, and with many top players still in the military late in World War II (Houtteman was too young for the draft), he made his major league debut on April 29. At 17 years old, he was the youngest player in the American League in the 1945 season before being optioned back to Buffalo, where on June 20 he threw seven no-hit innings, facing only 22 batters in the process, but lost the game 2–0 in extra innings. He also appeared in 13 games as a relief pitcher, and finished his minor league season with no wins, two losses and an ERA of 5.33 in just over 25 innings pitched.