Father’s Day took a back seat to the unofficial holiday of Pete Alonso Reinstatement Day in Mets land.

The Mets reinstated Alonso from the injured list prior to Sunday’s three-game series finale against the Cardinals at Citi Field.

The slugging first baseman originally was expected to miss 3-4 weeks with a bone bruise and sprain in his left wrist, but wound up missing only eight games.

Mark Vientos was optioned to Triple-A Syracuse to create room for Alonso.

The Mets were 3-5 without Alonso, who didn’t lose his lead among the National League home run leaders (22) while sidelined.