Cuellar got off to a 2–6 start in 1973, posting a 5.00 ERA through June 9. Afterwards, he went 16–7, posting a 2.56 ERA. He held the Texas Rangers to three hits on June 15 in a 1–0 shutout. Ten days later, he pitched all 12 innings of a 4–3 win over the Brewers. On July 19, he struck out 12 batters and pitched all 11 innings of a 3–1 victory over the Angels. He threw a five-hit shutout against the White Sox on August 18 in a 3–0 victory. From August 9 through September 1, he won six starts in a row; after losing on September 5, he won his last four decisions of the year. On September 17, he allowed four runs (two earned) and struck out nine as he pitched all 10 innings of a 5–4 win over the Yankees. In 38 starts, he had an 18–13 record, a 3.27 ERA, and 140 strikeouts in 267 innings. After a one-year absence from the playoffs, the Orioles won the AL East again, facing the defending World Series Champion Athletics in the ALCS. The starter for Game 3, Cuellar pitched every inning of an 11-inning game, matching pace with Ken Holtzman of the Athletics for 10 innings before finally giving up a game-ending home run to Bert Campaneris in a 2–1 loss. The Athletics won the series in five games.