He joined a bullpen that had been one of the worst in the major leagues, and during his rookie year won the closer job from a floundering José Mesa.

Sasaki's out pitch, a devastating split-fingered fastball that drops when arriving at home plate, was nicknamed "The Thang" by Mariners radio announcers.

In 2001, Sasaki had 45 saves, with 3.24 ERA in 69 games, and earned his first All-Star nod, as well as received down-ballot MVP votes.

Following that season, he decided to leave the Mariners before the last year of his contract in 2004, giving up $8 million, citing his desire to be with his family in Japan.

According to the Seattle Post-Intelligencer, however, Sasaki's real reason for returning to Japan was pressure from ownership, due to his "indiscreet philandering".

His last official appearance came as a cameo against the Yomiuri Giants on August 9, 2005, as he struck out his longtime friend and rival Kazuhiro Kiyohara in a game played at Fullcast Stadium Miyagi in his hometown.

Notable horses Sasaki has owned include Verxina, named by Enomoto,[8] who won the Victoria Mile twice,[9] Vivlos, winner of the Shūka Sho and of the 2017 Dubai Turf race on Dubai World Cup Night, and Cheval Grand, winner of the 2017 Japan Cup.