Along with fellow southpaw starters Charlie Hudson and Jerry Bark, he led the Mets to an 83–56 record,[2] and first place in the Carolina League Eastern Division.

A rhomboid muscle injury to Jerry Koosman opened a spot for a left hander in the Mets' starting rotation during the 1971 season.

Matlack made his major league debut against the Cincinnati Reds in the second game of a July 11 doubleheader, and was on the line for the victory when he departed after seven innings.

However, the Mets bullpen (including a blown save by Tom Seaver) was unable to secure the victory, and Matlack got a no decision in his major league debut.

[5][6][7] On May 8, 1973, a vicious line drive off the bat of Marty Perez of the Atlanta Braves struck Matlack's head so hard that the ball rebounded into the dugout.

He suffered a hairline fracture of his skull, but recovered quickly enough to return and pitch six shutout innings at Pittsburgh on May 19.

Perhaps his most memorable moment with the Mets occurred on October 7, 1973, when he held the "Big Red Machine" to just two hits in Game 2 of the 1973 National League Championship Series.

Matlack was dealt from the Mets to the Texas Rangers in the first four-team blockbuster deal in Major League Baseball history on December 8, 1977, that also involved the Atlanta Braves, Pittsburgh Pirates and a total of 11 players changing teams.

The Mets got from the Braves Willie Montañez and from the Rangers Tom Grieve and Ken Henderson who was sent to New York to complete the transaction three months later on March 15, 1978.

He rebounded to make 34 starts in 1980, one of which was on August 19, when he held George Brett, who was batting over .400, hitless, ending his 30-game hitting streak.

[15] Matlack compiled 1,023 strikeouts and a 3.03 earned run average as one of the "Big Three" pitchers the New York Mets were built around in the 1970s, along with Tom Seaver and Jerry Koosman.