A year ago at this time, Yankees General Manager Brian Cashman had to persuade Hal Steinbrenner, the team’s general managing partner, to take a most un-Yankee-like approach to the trade deadline, advising him to shed well-known and highly paid players in exchange for unproven prospects.

In other organizations, this is known as a fire sale, the baseball equivalent of raising the white flag on a season, and it generally signals that a club is about to start a rebuilding program, something the Yankees had not embarked on in more than 20 years.

This year Cashman reversed course, and on Monday he persuaded Steinbrenner to part with three of the Yankees’ most prized prospects in exchange for what he believes could be the final piece in yet another Yankees championship puzzle.

That piece is Sonny Gray, an accomplished right-handed starting pitcher, who came from the Oakland Athletics in a trade for three minor leaguers: infielder Jorge Mateo; the right-hander James Kaprielian, the Yankees’ first-round draft pick in 2015; and outfielder Dustin Fowler, who was called up to the major leagues in June only to sustain a ruptured patellar tendon chasing a foul ball in the first inning without even coming to bat.