Rule 5's terms dictated that the Angels keep Clark on their 25-man big-league roster for the entire 1967 season or offer him back to the Detroit organization, but Clark would earn his place in the Angels' starting rotation on merit. After he won his MLB debut on April 22 with four scoreless innings in relief against the Cleveland Indians, Clark made his first start eight days later against the New York Yankees; he went seven innings, allowed only four hits and two earned runs, and collected his second big-league triumph. ManagerBill Rigney then kept Clark as a regular member of the Angel starting staff through the remainder of the season, in which the Angels battled for the American League pennant before fading in September. Clark won 12 games, tying him with staff ace Jim McGlothlin and closerMinnie Rojas for the team lead in victories. His 2.59 earned run average also was best among Angel starters. He threw a two-hit, complete game shutout against the Washington Senators on September 8 at D.C. Stadium. It was his only complete game and shutout of the season.
Later MLB career
The following year,, saw Clark lose nine of his first ten decisions and drop out of the Angel starting rotation in early July. He worked in only 94 innings pitched, half of his 1967 workload, and finished the year with a 1–11 record. He then spent most of, all of, and the early weeks of in the minor leagues. But the Angels recalled him in June 1971, and in his third appearance and second starting assignment, Clark tossed another two-hit shutout, this time against the eventual division championOakland Athletics at Anaheim Stadium on July 2. Those two-hitters, almost four years apart, would be the only shutouts of his MLB career. Clark spent the entire season with the Angels, working in 26 games and hurling two more complete games. But he posted a 4–9 record and a 4.51 earned run average and during the offseason his contract was sold to the Philadelphia Phillies' organization, where he spent 1973 at Triple-A before leaving baseball. In 96 major leaguegames pitched, Clark won 19 games and lost 32 with a 3.38 career earned run average. In 431 innings pitched, he allowed 371 hits and 213 bases on balls, striking out 236.