The right-handed Eckersley had two very successful careers in baseball, as a starting pitcher from 1975 through 1986 and as a reliever from 1987 until his retirement after the 1998 season.

Eckersley became a full-time starter with the Cleveland Indians in 1975, his first major league season. After winning 40 games in three years, including a no-hitter against the California Angels on May 30, 1977, he was traded to the Boston Red Sox in 1978 and had a 20-8 record with a 2.99 ERA. He remained with Boston until 1984, when he was traded during the season to the Chicago Cubs.

From 1988 through 1992, Eckersley was the best closer in baseball. He led the American League in saves with 45 in 1989 and with 51 in 1992, when he won the Cy Young Award and was named the American League's most valuable player. Eckersley had a 7-1 record, a 1.91 ERA, and 93 strikeouts against only 11 walks in 80 innings of work that season.

In the 1988 league championship series, Eckersley saved every game as Oakland swept Boston. Unfortunately, he may be best remembered for the game-winning home run he gave up to the hobbled Kirk Gibson of the Los Angeles Dodgers in the first game of the World Series that year. The heavily favored Athletics lost the series in five games.

Eckersley went to the St. Louis Cardinals as a free agent in 1996. He finished his career back with the Red Sox in 1998. He was elected to the Baseball hall of Fame in 2004.