With the fifth starting spot in the rotation open in spring training for the 2014 campaign, Martínez started the season in the bullpen of the Major League Cardinals. Injury struck the rotation in June, and he made his first two starts of the year as spot starts. He made his third major league start and won his first on June 22, pitching five innings and yielding three earned runs in a 5–3 victory over the Philadelphia Phillies. In a July 3 start against the San Francisco Giants, he reached a breakthrough as a starter. In five innings, he allowed just one run on five hits, one walk and struck out six. At the plate, he collected a two-run batted in double as the Cardinals won 7–2, and Martínez collected his second win of the season. He finished the 2014 regular season with a 4.03 ERA and 2–4 W–L in 57 games including seven starts. In December, Martínez changed his uniform number from 44 to 18 to commemorate his friend and teammate, Oscar Taveras, who had died in a car accident two weeks after the 2014 NLCS.