When it comes to Brett Gardner, first-year Yankees manager Aaron Boone believes in metrics and makeup.

Even as Gardner’s batting average dipped under .200, Boone was optimistic. For starters, Gardner’s exit velocities and other advanced stats indicated a breakout was coming. Plus, the speedy leadoff man was still getting on base.

It wasn’t just the numbers, though.

Gardner capped a slump-busting performance with a go-ahead, two-run triple off Craig Kimbrel in the eighth inning, Aaron Judge followed with a homer and New York rallied to beat the Boston Red Sox 9-6 Wednesday night for its 17th victory in 18 games.

Kimbrel entered with two on and one out to face Gardner seeking the first five-out save of his career. Gardner drilled a full-count pitch into left-center, well over the head of center fielder Mookie Betts, who was playing shallow. Neil Walker scored easily from third and rookie Gleyber Torres raced from first and slid past a lunging tag attempted by catcher Christian Vazquez.

Judge followed with a line drive to center measured at 117 mph off the bat, his ninth homer of the season. He had three hits, three RBIs and a diving catch in right field as New York won its eighth straight overall and 11th in a row at home.

New York (26-10) broke a tie with Boston for first place in the AL East and has sole possession of the best record in the majors for the first time since July 27, 2012. The Yankees are on a 35-8 tear in the Bronx since Sept. 2, including the postseason, and at 16-5 have the best home record in the majors this year.

Fans at a sold-out Yankee Stadium went wild in the eighth. Judge compared it to the postseason atmosphere last October, and the party spilled over onto River Avenue so loudly it could still be heard back inside the stadium 15 minutes after the game.

Aroldis Chapman pitched the ninth for his ninth save. J.D. Martinez got a hit off Chapman and ran into the closer trying to round first base. Martinez argued for interference, but the umpires held him at first on a grounder hit inside the bag. Chapman struck out Mitch Moreland to end it.

The Yankees had walk-off wins in three of their previous five home games. This rally came an inning earlier.

Kimbrel replaced Matt Barnes (0-1) after a double by Walker and a one-out walk to Torres. It was the second blown save in four appearances for Kimbrel, who recently became the fastest reliever to 300 career saves.

Red Sox manager Alex Cora said the team had planned to be aggressive with Kimbrel because he hadn’t pitched since Saturday.

“Today was the day we were like, ‘You know what? He’s rested enough and we know they’ve been coming back against a lot of teams,’” Cora said.

Hanley Ramirez put Boston ahead 6-5 with a two-run homer in the seventh. Ramirez turned on a hanging slider from reliever Chad Green and crushed it deep into the second deck in left field for his fourth homer.

Giancarlo Stanton drove in two with a go-ahead double off Rick Porcello in the third inning a day after hitting a pair of solo homers in a 3-2 Yankees victory. It was the first time Stanton had RBIs in consecutive games this season, and he improved to 10 for 19 with seven RBIs against Boston during his first season in pinstripes.

Moreland and Andrew Benintendi homered as Boston chased Masahiro Tanaka after 5 1/3 innings. Tanaka allowed four runs.

Yankees reliever Jonathan Holder (1-1) cleaned up a mess left by Chasen Shreve in the eighth, getting Benintendi to ground out with the bases loaded.

Porcello allowed five runs in 5 1/3 innings — his first time giving up three or more runs this season.

TRAINER’S ROOM — Red Sox: LHP David Price was diagnosed with carpal tunnel syndrome after twice experiencing numbness in his pitching hand this season. Cora called it “good news compared to anything else.” Price will throw at Yankee Stadium on Thursday before being re-evaluated.