When he experienced a second-half swoon, Aaron Judge didn’t change no matter how much it hurt to let down his teammates. When the start to his first postseason experience was a frigid one, Judge didn’t go searching for clues.

That mindset paid off in a big way Monday night in Game 3 of the ALCS, when Judge crushed a three-run homer in the fourth inning that carried the Yankees to an 8-1 must-have-victory over the Astros in front of 49,373 at Yankee Stadium.

“I get a chance to play in the ALCS with the New York Yankees. It’s a dream come true,’’ said Judge, who added two sensational catches to help the Yankees reduce the Astros’ lead in the best-of-seven series to 2-1.

Game 4 is Tuesday when the Yankees will start Sonny Gray looking to even the series. Lance McCullers Jr. goes for the Astros.

Judge started the game hitting .129 (4-for-31) with 19 strikeouts and added a 20th punchout in the first inning when he swung through an 0-2 pitch from Charlie Morton. A walk on a 3-2 pitch in the third was followed by him smoking a 2-2 pitch for a line-drive homer that highlighted a five-run fourth inning and provided CC Sabathia room to cruise.

Todd Frazier had gotten the Yankees headed in the right direction with a three-run homer off Morton in the second inning.

Sabathia provided six scoreless innings in his 22nd postseason start. Adam Warren followed with two innings in which he didn’t allow a run. Dellin Betances’ control problems continued when he walked the first two batters in the ninth with an 8-0 lead and was replaced by Tommy Kahnle.

As for Judge, he absorbed much of the blame for the Yankees being limited to two runs in two losses in Houston even though nobody else dented Dallas Keuchel and Justin Verlander in Games 1 and 2.

As he did during the regular season when he hit 52 homers, Judge never changed mentally. Nor did he overhaul a swing that at times looked helpless against low breaking balls.

But when Harris left a pitch up Judge made him pay.

“He has a good cutter and a good curveball,’’ Judge said. “I am trying to see a cutter up in the zone and try to do damage on it in that situation. Just try to get a pitch up and do some damage.’’

Sabathia waltzed through the first two frames and retired the first two batters in the third before running into trouble. He walked George Springer, gave up a single to Alex Bregman and walked Jose Altuve to load the bases for Carlos Correa with a 3-0 lead.

“I was trying to make a pitch. He likes to get his hands extended,’’ Sabathia said of Correa, who killed the threat by popping up to Didi Gregorius. “I was trying to get something in on him and made a good enough pitch where he popped it up.’’

Sabathia was the beneficiary of Judge robbing Yuli Gurriel of an extra-base hit in the fourth when the right fielder crashed into the wall and fell to the ground after making a sensational catch. Judge also took a hit away from Cameron Maybin with a head-first dive toward the infield in the fifth.

“That was a great play. Off the bat with a short right field I didn’t know what the result was going to be,’’ Sabathia said of Judge getting to Gurriel’s ball. “For him to go all out and make that catch was unbelievable.’’

For Frazier, the night was something he wished everybody could experience.

“This is where you want to be. If you don’t want to play in this situation you don’t play this sport,’’ said Frazier, who pointed to his family and friends as he trotted between first and second bases. “Every baseball player’s dream.’’