Phil Mickelson carded a 69 and closed on 14-under 271 to win his second World Golf Championship title at Sheshan International Golf Club. Ernie Els, who also shot a 63, placed in second another stroke back.
Maruyama, who teed off in a tie for 32nd, made eight birdies, one bogey and an eagle on his last hole to finish at 10-under. Compatriots Ryo Ishikawa (70) and Komei Oda (68) shared 17th a shot behind.
Yuta Ikeda (72) tied for 51st at 1-over but remained at the top of the JGTO money list, about 600,000 yen ahead of Ishikawa. Shingo Katayama (65) closed in a tie for 33rd at 3-under.
World No. 1 Tiger Woods dropped into a tie for 6th at 12-under.