TOKYO—The Dodgers dipped into a familiar well of talent to bolster their pitching rotation this winter when they signed Japanese ace Kenta Maeda to an eight-year contract. The reigning Sawamura Award winner, given to Japan’s best pitcher, became the sixth player from Japan to make his major-league debut in Dodger blue, the most for any team besides the Seattle Mariners (also six) and the Dodgers’ New York progeny, the Mets (eight). Five starts later, Maeda takes a 3-1 record and 1.66 ERA into his Wednesday night appearance against the Mets in Los Angeles—a fitting commemoration of the now 60-year relationship between...