Lefferts helped the Padres win the 1984 National League pennant and the Giants win the 1987 National League West division title and the 1989 National League pennant. In the winter of 1985 he was offered to the New York Mets in exchange for outfielder Lenny Dykstra, but Mets general manager Frank Cashen declined the offer. The 83 games he pitched in during 1986 not only led the National League but remains a Padres single season record.