[8] Ahead of the 2010 season, Sakai was promoted to Kashiwa Reysol's first team, where he signed a contract with the club and was given the number 30 shirt.

[10] It wasn't until on 5 May 2010 when he made his Kashiwa Reysol debut, coming on as a substitute for Yohei Kurakawa in the 77th minute, in a 1–1 draw against Ventforet Kofu.

[15] Ahead of the 2011 season, the club announced that Sakai were among players to agree to stay at Kashiwa Reysol and was given a number 4 shirt.

[21] Sakai later helped Kashiwa Reysol win the league and lifted the trophy after beating Urawa Red Diamonds 3–2 in the last game of the season.

[30] Three days after winning the Japanese Super Cup, he scored his first goal of the season in the AFC Champions League, in a 3–2 loss against Buriram United.

[35] With his move to Hannover 96 reached an agreement, Sakai made his last appearance for the club, which came on 30 June 2012, in a 6–2 win over Gamba Osaka.

[48] In a follow–up match against local rivals’ Eintracht Braunschweig on 8 November 2013, he started and played the whole game to keep a clean sheet, in a 0–0 draw.

[74] Sakai made his Olympique de Marseille debut in the opening game of the season, where he set up a goal for Florian Thauvin, in a 4–0 win over Toulouse.

[90] On 12 April 2018, he scored his first UEFA Europa League goal on his 28th birthday in the quarter–final return leg, in a 5–2 win over RB Leipzig to progress into the next round and a 5–3 aggregate victory.

[92] Despite recovering from his injury in mid–May, he, however, was featured on the substitute bench throughout 90 minutes, as Marseille lost 3–0 to Atlético Madrid in the UEFA Europa League Final.

[97] After spending a month with Japan in the AFC Asian Cup, Sakai made his first appearance for the club, starting a match, in a 1–0 win against Girondins de Bordeaux on 5 February 2019.

[105] Ahead of the 2019–20 season, Sakai was linked with a move to Premier League side Tottenham Hotspur, but he ended up staying at the club.

[114] However, Sakai found himself suspended on two occasions, including one when he received a second bookable offence, in a victory against Trélissac on penalties following a 1–1 draw in the third round of Coupe de France.

[120] During a match against Paris Saint-Germain on 13 September 2020, he was caught in the centre of attention after Spanish radio station Cadena SER claimed to have footage of Neymar racially abusing him.

[128] However, his return was short–lived when Sakai received a straight red card at the last minute for a foul on Kader Bamba, as Marseille drew 1–1 against FC Nantes in a follow–up.

[130] Despite suffering sciatica problems on three separate occasions later in the 2020–21 season, Sakai made two starts, playing either centre–back position, winning both matches.

[143] On 10 April 2022, Sakai made his return from injury, starting a match, against FC Tokyo and helped Urawa Red Diamonds kept a clean sheet, in a 0–0 draw.

[157] But Sakai was able from injury when he led Urawa Red Diamonds secured a dramatic victory in the 2022 AFC Champions League final.

Sakai led Urawa Red Diamonds' captain to beat the defending champions Al Hilal 2–1 on aggregate, making it their third win in the competition.

[173] On 11 June 2024, it was reported by Andy Harper that Sakai agreed with a move to Auckland FC for their inaugural A-League Men's season.

[178] Three weeks later on 23 June 2011, Sakai scored his first goal for the U23 side, in second leg of the Asian Qualifiers Preliminary Round of the Summer Olympics, in a 2–1 loss against Kuwait U23, but Japan U23 won 4–3 on aggregate.

[184] Sakai was named as one of Japan's three over-age players for the Olympic on home soil, alongside Maya Yoshida and Wataru Endo.

[189] After eight months since being called up to the Japan’s national team, Sakai made his debut for the Samurai Blue, coming on as a second–half substitute, in a 2–0 win over Azerbaijan in the Kirin Challenge Cup on 23 May 2012.

[191] For the rest of 2012, Sakai continued to get more playing time for Japan, including making his first start for the Samurai Blue against United Arab Emirates on 6 September 2012.

[196] Following the conclusion of the FIFA Confederations Cup tournament, he then started the next six Japan international matches in the absence of Uchida, who suffered a torn tendon and was eventually out for the 2013–14 season.

[203] After Uchida's absent in recent matches of 2015, Sakai began to make an impact to keep his first team place for Japan.

[209] He started the next two matches for Samurai Blue, and eventually qualifying for the knockout stage, due to receiving fewer yellow cards than Senegal, becoming the only Asian team to do so in the 2018 World Cup.

[217] In the AFC Asian Cup final against Qatar, Sakai started the match in the right–back position, as Japan loss 3–1, finishing as runner–up in the process.

[220] On 1 October 2020, Sakai was called up to the Japan’s squad for the first time in eleven months, resulting in him making an appearance against Cameroon, drawing 0–0.

[227] His next appearance for the Samurai Blue came against Croatia on 5 December 2022, coming on as a 75th-minute substitute, as the match eventually ended 1–1 with Japan crashing out after their defeat on penalties.