Sanguillen was a close friend of his teammate Roberto Clemente. In 1972, Sanguillen, who had been playing winter baseball with the San Juan Senators, spoke to Clemente about accompanying him on a relief mission to Nicaragua. Sanguillen missed the plane because he had misplaced his car keys; he was devastated when he learned that the plane had crashed, killing Clemente. Against the advice of Pirates General Manager Joe Brown, Sanguillen insisted on helping to recover the bodies of those who died in the crash. The sight of many sharks swimming in the water did not stop Sanguillen. As Pirates teammate Steve Blass told "The Sporting News", "Manny dove from dawn till midnight." So focused on his task was he that he missed the January 4 memorial service attended by his Pirate teammates.