David Ortiz is retiring why exactly? Big Papi didn’t look ready to hang ’em up Sunday night when he continued to torment the Yankees with a pair of home runs in Boston’s 5-1 victory at Yankee Stadium.

Ortiz, 40, is batting .308 with nine home runs and 27 RBIs in what he continues to insist will be his final season.

The Yankees, and their fans, will be happy to see him go.

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“I’m retiring,” Ortiz said when asked if he might change his mind at the end of the season. “It’s very set in my mind right now.”

But why?

Said Red Sox manager John Farrell: “It probably crosses all of our minds, given the start that he’s off to. In this ballpark, he’s extremely dangerous for obvious reasons with the dimensions, but he’s in such a good groove. So many balls are squared up, hit hard. He’s having fun. He’s having fun playing.”

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Ortiz had more fun Sunday night than he did on Friday night, when he was ejected after getting called out on strikes with the bases loaded in the ninth inning of the Yankees’ 3-2 victory. Big Papi was not a jolly soul as he rushed out of the dugout and jawed with plate umpire Ron Kulpa. But he was back to his cuddly self Sunday after going deep twice off Luis Severino.

Ortiz hit a monster blast to right in the fourth and another home run to right in the seventh. The two solo shots gave him 52 home runs against the Yankees (51 with the Red Sox, one with the Twins).

Ortiz tied former Red Sox great Carl Yastrzemski for the fifth-most home runs against the Yankees. He also passed Yaz for second place on the all-time Red Sox home run list with No. 453, behind only Ted Williams (521).

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“I’m not really paying attention to any of that,” Ortiz said. “I can still hit the ball and do what I do and I’m going to continue playing the game.”

Until the end of the season, that is. He has six more regular-season games scheduled at Yankee Stadium, with the last one set for Sept. 29.