Soonafter, when asked if he preferred the new AstroTurf on the field at the Houston Astrodome to real grass, he said, "I don't know, I never smoked AstroTurf." McGraw made the team as a reliever, and was 0–1 with a 3.12 ERA and one save when he made his first major league start on July 28 against the Chicago Cubs in the second game of a double header at Wrigley Field. He Lasted just two-thirds of an inning and gave up three earned runs on his way to a 9–0 loss (the Cubs blew the Mets out in the first game as well, 7–2). On August 22, in his second start, also in the second game of a double header, only this time against the St. Louis Cardinals at Shea Stadium, McGraw pitched a complete game to earn his first major league win. He won his next start as well, 5–2 over Sandy Koufax and the Los Angeles Dodgers. It marked the first time the Mets had ever beaten the future Hall of Famer. McGraw remained in the Mets' starting rotation for the remainder of the season, however, failed to log another win, going 2–6 as a starter, and 0–1 in relief. The Mets used McGraw as a starter again in 1966, and he was 2–9 with a 5.52 ERA in that role. Though he also made four starts with the Mets in 1967, McGraw spent most of the season, and all of 1968 in the minor leagues with the Jacksonville Suns. By the time he returned to the Mets in 1969, manager Gil Hodges had a very capable young pitching rotation that included Tom Seaver, Jerry Koosman, and Gary Gentry and had no need for McGraw as a starter until Koosman went down with an injury in May. McGraw went 1–1 with a 5.23 ERA filling in for Koosman. Koosman returned to the rotation at the end of the month and on May 28, after a five-game losing streak that saw the Mets fall into fourth place in the newly aligned National League East, Koosman and the expansion San Diego Padres' Clay Kirby engaged in a pitchers' duel at Shea. After nine scoreless innings by Kirby and ten by Koosman, the game was turned over to the bullpens for extra innings. The game finally ended after 11 innings when Bud Harrelson hit a single to drive in Cleon Jones.