Denny McLain in 1968. Before that the last one was Dizzy Dean in 1934. Lefty Grove did it before that in 1931 and twice in the twenties, as did Grover Cleveland Alexander. Apart from that you have to go back to the dead-ball era. The most wins any pitcher had even coming close to that since then was 27 by Steve Carlton in 1972 and Bob Welch in 1990.
Before that you'd have to go back to 19th Century when teams rarely carried more than three or four pitchers on their roster. Win totals for pitchers were often 30 or more with Hoss Radbourne winning 60 games in one season, a record that is unlikely to ever be broken. With the 5 man pitching rotation today, it will likely never happen again. As a pitcher would be lucky to even get 30 starts in a season.
Grover Cleveland Alexander of the Philadelphia Phillies who won 31 in 1915, 33 in 1916, and 30 in 1917.
Through games played on April 28, 2001 that was Jon Lester on June 27, 2010 ... a 9-3 win over the San Francisco Giants
Bob Welch of the Oakland Athletics was the last pitcher to win 25 or more games in a season. In 1990, Bob Welch won the American League Cy Young Award with a 27-6 record.
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Wilbur Wood of the Chicago White Sox was 24-20 during the 1973 season, making him the last pitcher in American League history to win and lose 20 or more games in the same season.
Ryan Dempter
Randy Johnson!!
In 1968, Tigers' pitcher Denny McLain ended the regular season with a record of 31-6. He is the last pitcher in MLB history to win 30+ games in a season.
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As of the 2013 season, the last MLB pitcher to win 30+ games in a season was Denny McLain of the Detroit Tigers who went 31-6 in 1968.
Jim 'Catfish' Hunter who pitched 30 complete games for the 1975 New York Yankees. In the last 50 years other than Hunter, Steve Carlton pitched 30 complete games for the 1972 Philadelphia Phillies, Ferguson Jenkins pitched 30 complete games for the 1971 Chicago Cubs, and Juan Marichal pitched 30 for the 1968 San Francisco Giants.
the brewers retired their bullpen harley davidson, complete with a sidecar for the incoming pitcher, after the 1995 season.
Bob Welch of the Oakland Athletics was the last pitcher to win 25 or more games in a season. In 1990, Bob Welch won the American League Cy Young Award with a 27-6 record.
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Wilbur Wood of the Chicago White Sox was 24-20 during the 1973 season, making him the last pitcher in American League history to win and lose 20 or more games in the same season.
Mike Mussina was the last Yankees pitcher to win 20 games in a season. In 2008, Mike Mussina's record was 20-9.
Cardinals Dizzy Dean in 1934, 30 victories.