Thanks to his strong finish in 2012, Kendrick entered spring training assured of a spot in the Phillies' Opening Day starting rotation for the first time in five years and spent his first full season exclusively a member of the major league starting rotation. His 2013 season took the opposite trajectory of his 2012 campaign; he held a 4–1 record with a 2.47 ERA in his first eight starts, while he posted a 6–12 record with a 5.65 ERA in his final 22 starts. Some suggested that because Kendrick is a contact pitcher (i.e., he focuses on getting outs via batters hitting the ball rather than striking out), his career-worst batting average on balls in play indicated horrendous defense was the primary reason for his downturn, not necessarily poor pitching. However, both were likely contributing factors. On September 18, he was scratched from his scheduled start due to right rotator cuff tendinitis, which may have contributed to his poor pitching down the stretch. It was the first time in Kendrick's career he missed a start due to injury. He had initially planned on making his next start, but the Phillies announced on September 20 that Kendrick had been shut down for the remainder of the season after receiving a second opinion on the injury. The team placed him on the disabled list for his first career stint and Zach Miner took his spot in the rotation. Overall, he posted 10–13 with a 4.70 ERA in 182 innings pitched.