Sakai Hideyuki (坂井 秀至, born April 23, 1973) is a Japanese 8 dan professional. He is currently a top professional in Japan, but is also notable for having had a long amateur career before qualifying as a professional. He was one of the first to be awarded an amateur 8-dan diploma. In 2000 he won the World Amateur Go Championship, and was accepted as a professional by the Kansai Ki-in in the following year. As part of the qualification procedure, he played four testing games against professionals and won them all. He was immediately awarded a 5 dan professional rank at the age of 28.
Prior to becoming pro, he was a medical junior resident.
In 2019, Sakai decided to resume his medical career; he announced he was taking an unlimited leave of absence from all tournaments.
- Sakai was the first Japanese amateur to beat a 9 dan in an even tournament game. His opponent was Ishii Kunio, in the 1999 Agon Kiriyama Cup.
- Winner of the World Amateur Go Championship in 2000
- November 20th, 2003 : Sakai Hideyuki 6 dan won the 47th Kansai Ki In First Place Championship beating Yukawa Mitsuhisa 9 dan by 2-1.
- In 2007-2011 he had berths in the Meijin league, with 3rd, 5th and two 4th place finishes.
- August 27th 2010: Sakai Hideyuki 7 dan won the 35th Gosei, defeating the titleholder Cho U by 3-2. Of the professionals who qualified after age 20, he's the first who challenged for one of the top titles.
- 2011 was a less successful year for Sakai Hideyuki, he finally lost his berth in the Meijin league, and could not defend the Gosei title against challenger Hane Naoki, who made a comeback after Sakai Hideyuki took an early 2:0 lead in the match. In November 10th, Sakai won the 55th Kansai Ki In First Place Championship, beating the previous champion Murakawa Daisuke 7 dan by 2-0.
- In 2012-10-04, Sakai won the 56th Kansai Ki In First Place Championship, again beating Murakawa Daisuke 7 dan by 2-0.
- In 2013-09-19, Sakai won the 57th Kansai Ki In First Place Championship, beating Furuya Yutaka 8 dan by 2-0.