Yasui Sanchi (安井算知, 1617-1703) was a Japanese professional go player, and second head of the Yasui house.
He became Meijin-godokoro in 1668. It has always been said that this promotion was achieved by a backstairs route, with influence exerted by the head of the Matsudaira clan. A related anecdote has Honinbo Sanetsu facing down Lord Matsudaira during an earlier official oshirogo against Sanchi.
The Honinbo house did not take this lying down. From 1668 to 1675 Honinbo Doetsu played a twenty game match against Sanchi (they had played in 1649, but after that there was a dearth of competitive games). Doetsu had the better of it with Black, earning the right to a game with White (as at sen-ai-sen).