Bob Welch, then of the Los Angeles Dodgers, pitches in a 1978 game against the Philadelphia Phillies. Mr. Welch won the American League Cy Young Award in 1990. He died June 9 at 57. (Rusty Kennedy/AP)

Bob Welch, one of the first professional athletes to admit to alcoholism, and who had one of baseball’s most magical pitching seasons in 1990, when he won 27 games for the American League champion Oakland Athletics, died June 9 at his home in Seal Beach, Calif. He was 57.

Police officers reportedly found Mr. Welch dead in the bathroom of his house. The cause of death is pending an autopsy.

Mr. Welch had an auspicious rookie season with the Los Angeles Dodgers in 1978, when he joined the team midway through the season. He pitched three shutouts, including one to clinch the division championship, as the Dodgers went on to win the National League title.

In the second game of the 1978 World Series in Dodger Stadium, Mr. Welch struck out New York Yankees slugger Reggie Jackson in the ninth inning to preserve a 4-3 Dodgers victory. The Yankees eventually won the series in six games, but Mr. Welch’s heroics became a permanent part of Dodgers lore.

“It was all downhill after that,” Mr. Welch later said of his life after the World Series.

During a mediocre season in 1979, it became apparent that he was suffering from more than a poor year on the mound. He drank in the clubhouse, had alcohol-induced blackouts and challenged opposing players to fights. After being confronted by his teammates and club officials, he spent 36 days at a treatment facility in Arizona.

In his 1981 book, “Five O’Clock Comes Early,” written with New York Times sportswriter George Vecsey, Mr. Welch described his struggles with alcohol, which he said began when he was 16. It marked one of the first times an active professional athlete openly discussed a drinking addiction.

“I would get a buzz on and I would stop being afraid of girls,” Mr. Welch wrote. “I was shy. . . . But with a couple of beers in me, it was all right.”

Along with his personal recovery, Mr. Welch’s pitching quickly rebounded. He had several fine years with the Dodgers, was an all-star in 1980 and helped the team win a World Series championship in 1981.

After being traded to Oakland before the 1988 season, Mr. Welch became a prominent member of a team that won three straight American League pennants. He won 17 games in 1988 and again in 1989. He was scheduled to start Game 3 of the 1989 World Series against the San Francisco Giants when an earthquake shook the Bay Area minutes before the opening pitch.

With the series postponed for almost two weeks, Oakland Manager Tony LaRussa turned to other pitchers in the team’s rotation, and the A’s won the World Series in four games. Mr. Welch never threw a pitch in the series.

The next year, he pitched poorly in spring training, then gave up a home run to the first hitter he faced in the regular season. At 33, he was seemingly in the twilight of his career.

From then on, though, he had one of the most remarkable seasons of any pitcher in the past 45 years. He reeled off one victory after another and was the American League’s starting pitcher in the All-Star Game.

He ended the season with a record of 27-6, the most wins by any pitcher since Hall of Famer Steve Carlton won 27 for the Philadelphia Phillies in 1972.

Mr. Welch, who also had an earned run average of 2.95, won the Cy Young Award as American League’s best pitcher. The A’s won 103 games in 1990, but they were stymied in the World Series, losing in four games to the Cincinnati Reds.

Although Mr. Welch pitched for four more years, he never again close to his stellar season in 1990 — but then, neither has anyone else. Since then, no other big-league pitcher has won more than 24 games in a season.

Robert Lynn Welch was born Nov. 3, 1956, in Detroit and grew up in a blue-collar suburb. His father worked in an airplane factory.

Mr. Welch was a baseball star in high school and at Eastern Michigan University before signing with the Dodgers. During 17 seasons in the majors, the 6-foot-3 right-hander had a record of 211-146, with a 3.47 ERA.

In 2001, Mr. Welch was the pitching coach of the World Series champion Arizona Diamondbacks. In recent years, he worked as a spring-training coach with Oakland.

Survivors include his wife of 30 years, the former Mary Ellen Wilson; and three children.

During the final month of his 27-win season in 1990, Mr. Welch said he learned an important lesson about pitching during his recovery from alcoholism.

“I’m only trying to approach baseball with the same attitude I have learned to approach life,” he said, “one day at a time.”