Sakai started playing football at Sanjō junior soccer club, together with his brother Noriyoshi.

At age 15, he joined Albirex Niigata youth academy and entered Kaishu Gakuen High School.

He made his Albirex first-team debut, at the age of 17, on 15 November 2008 in the Emperor's Cup match against FC Tokyo.

[2][3] On 11 February 2012, Sakai made his Bundesliga debut for VfB Stuttgart in a 5–0 home victory against Hertha BSC.

[4] Sakai scored his first goal for Stuttgart on 22 November 2012 in a 5–1 away victory against FC Steaua București in the 2012–13 UEFA Europa League group stage.

In 2011, he was named in Japan's final 23-man squad to compete at the 2011 AFC Asian Cup in Qatar but had to withdraw due to an injury.

[14] He made his debut for the Japan senior national team on 6 September 2012 in the Kirin Cup against the United Arab Emirates.