By his own admission, there’s no secret as to how or why Chase Headley has been the Yankees’ hottest hitter since a dreadful month of May.

“Really, after May, I thought I was swinging the bat pretty well,” said Headley, whose line-drive double into the right-centerfield gap off Michael Fulmer drove in two runs in the fourth inning in the Yankees’ 7-3 victory over the Tigers on Monday night at Yankee Stadium. “I had a really, really tough May, obviously, but from then on, it felt like I was swinging the bat pretty well. Obviously, the better you swing it, you get some results and you get confident and things can build. That’s really it. There’s no secret.”

The month of July was kind to Headley, now the Yankees’ first baseman since the trade for third baseman Todd Frazier in mid-July. He hit .333 (30-for-90) in 26 July games and has batted .429 (15-for-35) since moving to first base. In his final July game, he went 3-for-4 against the Tigers.

The 33-year-old produced a slash line of .165/.211/.235 in 23 May games, but aside from that, Headley has been a reliable contributor for a Yankees team that leads second-place Boston by a half-game in the AL East.

Overall, Headley is hitting .274 with 42 RBIs and has performed particularly well against righthanded pitchers. Entering Monday, he had a .291/.391/.423 slash line as a lefthanded hitter and a .218/.248/.307 slash line as a righthanded batter this season.

“He’s been great,” Joe Girardi said. “He’s swung the bat great. It even started a little bit before the All-Star break, for me. He went through the tough period, but golly, he’s swinging the bat really well, and he’s adapted to first base really well.”

An abrupt midseason position change easily could have had a negative impact on Headley’s production, but the 11-year veteran has taken the move in stride. He has yet to make an error at first base in 13 games (eight starts).

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“It’s been different,” Headley said. “I’m trying not to overthink things, for the most part, just catch the ball like I’ve always done. I think it’s gone pretty well so far. I’m sure there are some things that are going to come up that I’m going to have to adjust to, but for the most part, I feel like I can catch ground balls and make flips and catch the throws from everybody else.”

Headley said he tries “to keep offense and defense separate,” but he’s riding highs on both sides of the ball as the calendar shifts to August with the team in a pennant race.

Headley had a .301/.402/.494 slash line in April, but after his dreadful May, some fans were writing him off and clamoring for top prospect Gleyber Torres, who has since had Tommy John surgery. But beginning June 1, Headley has hit .316 (54-for-171).

“He swung the bat so well in the first month, he was in a great place, then he struggled,” Girardi said. “I think he just found himself again.”