He became the team's starting shortstop by the fall of his first year (the equivalent of tenth grade in the United States) at Kosei Gakuin High.

[5] In 2008, Manager Tatsunori Hara had high hopes for Sakamoto in the 2008 season, playing him in all 15 pre-season (spring training) games at either shortstop or second base.

[6] Although Sakamoto was expected to platoon at second base with the likes of veteran journeyman Kimura Takuya and speedster Ryota Wakiya throughout the season, he returned to his natural position when Nioka tore his right calf muscle in that very game.

Sakamoto finished the season with a .257 batting average, eight home runs, 43 RBI and 10 stolen bases, contributing to the Giants' league title that year.

[10] He made his first appearance in the Japan Series against the Saitama Seibu Lions on November 1, hitting a home run off veteran right-hander Fumiya Nishiguchi in Game 7[11] and becoming the first NPB player in 22 years to hit a home run in the Japan Series while being under the age of 20 (Kiyohara Kazuhiro last accomplished the feat while he was with the then-Seibu Lions).

[12] In 2009, Sakamoto got off to a good start to the 2009 season (his third in the pros and second at the major league level), hitting .376 with a league-leading 11 doubles and slugging .541 for the month of April.

He hit the first walk-off home run of his career on May 6 off reliever Hiroki Sanada (who was a teammate of Sakamoto until he was traded midway through the 2008 season) in a game against the Yokohama BayStars.

Like most of his teammates, he had problems at the batting plate, as he was unable to hit for consistency during the pool rounds, though he had a crucial RBI single equalizer against Chinese Taipei in the bottom of the 8th of that game.

Sakamoto seemed to regain his batting sense alongside his teammates in the 16-4 mulling of the Netherlands that qualified Team Japan to the semi-finals, hitting 2-5 in the game including a grand slam in the top of the 7th that gave Japan a more than 10 run lead needed to end the game early via mercy rule, securing an early ticket to the semis.

Though the majority of his extra-base hits tend to be line drives into the alleys (37 doubles in 653 career at-bats as of May 13, 2009), many predict that Sakamoto will develop home run power as his body fills out.

[citation needed] Sakamoto puts his superb athleticism (he was clocked at 6.0 seconds in the 50-meter dash and 110 meters in the long toss in high school) to good use in the field.