The first external hire of MLB’s managerial cycle is set to become a stunner.

President of baseball operations Buster Posey and the Giants are “moving toward” hiring Tennessee head coach Tony Vitello, The Post’s Jon Heyman confirmed.

The Athletic first reported the development.

Vitello, when contacted by the outlet, responded, “There is nothing to confirm,” and the Knoxville News Sentinel reported that he addressed the Volunteers in right field following a fall scrimmage and talked about the reports linking him to the Giants.

If the Giants agree on a deal with Vitello, a decision would occur at some point over the next 24 to 72 hours, according to ESPN.

He would leave the national powerhouse he helped build — guiding Tennessee to the 2024 national championship — and take over the position that opened when the Giants fired Bob Melvin, becoming the first manager in history to go from a college coach to a professional manager without any previous MLB jobs, ESPN reported.

“He’s the guy who probably convinced Buster Posey he could beat the Dodgers,” an anonymous source told the San Francisco Standard. “No doubt in my mind that he walked in and said that. Just give me the horses.”

Vitello, 47, has never served as an MLB coach before, with the former Missouri infielder working as an assistant for the Tigers, TCU and Arkansas before getting hired as the Volunteers’ head coach ahead of the 2018 season.

Tennessee has advanced to either the super regional or the College World Series in each of the last five seasons, with its initial CWS appearance under Vitello marking the program’s first since 2005.

Vitello bolting for the Giants would add a shocking jolt to the managerial hiring process, and given his reported salary of $3 million at Tennessee, The Athletic added that he could instantly become one of the highest-paid managers.

The Rangers made the first managerial decision of the cycle when they moved Skip Schumaker — who led the Marlins from 2022-24 and was most recently a senior advisor to president of baseball operations Chris Young — from their front office to the bench, while the Padres, Braves, Angels and Twins still have openings to fill.