The Amazin’s are acquiring right-handed reliever Ryan Helsley from the Cardinals in a trade, The Post’s Jon Heyman reported. Three prospects are going back to St. Louis: infielder Jesus Baez and pitchers Nate Dohm and Frank Elissalt.

Ryan Helsley, the fireballing two-time All-Star closer and longest-tenured member of the St. Louis Cardinals, recently estimated his chances of being traded away at “90 percent.” He was proven correct on Wednesday when he was traded to the New York Mets.