The Costa Rican somehow managed to scoop the ball over an open goal from five metres as Sporting pressed forward in a bid to wipe out Kostas Mitroglou's first-half goal for champions Benfica.
It was the first time Benfica had beaten their neighbours since former coach Jorge Jesus joined Sporting in a move that shocked Portuguese football in May.
Jesus, who led Benfica to the last two league titles, has defeated his old club this season in the Supercup, the Portuguese Cup and in their first league meeting of the campaign when Sporting won 3-0 at the Stadium of Light.
Saturday's encounter was billed as a grudge match between Jesus and his successor Rui Vitoria.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
In January, Jesus dismissively said he did not consider Vitoria to be a coach and that "he is not my colleague".
Benfica made a confident start and took a deserved lead in the 21st minute when Andreas Samaris' ball into the area hit Sporting midfielder William Carvalho and fell invitingly for Mitroglou to beat keeper Rui Patricio.
The visitors were missing goalkeeper Julio Cesar through injury but he was ably replaced by fellow Brazilian Ederson.
Jefferson crashed a long-range shot against the crossbar as the home team came alive just before halftime.
Sporting took control in the second half and Ruiz spurned a good chance when an Islam Slimani cross found him unmarked at the far post and he failed to control the ball.
That miss was completely overshadowed soon after when Slimani again found Ruiz and this time he lifted the ball over the bar when it was easier to score.
Ruiz nearly made amends one minute later with a dinked effort which Ederson did well to turn away.
Benfica midfielder Renato Sanches was lucky not to be sent off for a wild lunge at Ruiz and Sporting captain Adrien Silva, who had already been substituted, was sent off from the bench for protesting against the decision.
The win left Benfica with 61 points from 25 matches, two more than second-placed Sporting.
(Writing by Brian Homewood; Editing by Tony Jimenez)
