BOSTON — Welcome to the American League Championship Series, or as they’re calling it in The Bronx, the Yankees’ worst nightmare.

Argue all you want about the baseball postseason’s small sample sizes. I sure as heck do. Nevertheless, the stark reality of the moment speaks for itself:

The Red Sox and Astros, who kick things off Saturday night with Game 1 at Fenway Park, put up the two best records in Major League Baseball this season.

They are the last two teams to end the Yankees’ season, the Red Sox doing so last week in the AL Division Series and the Astros outlasting them in last year’s ALCS.

The survivors of this terrific matchup will qualify for their second World Series since the Yankees last made the Fall Classic in 2009, as the Astros are the defending champions and the Bosox won it all in 2013.

The truth can hurt.

“It’s going to be fun,” Astros third baseman Alex Bregman said. “You’ve got two of the best fan bases in baseball, two of the best pitching staffs, two of the best offenses going at it.”

The Red Sox, with 876 runs scored in the regular season, have the best offense. The Astros, having allowed only 534 runs, field the best pitching staff. The Astros’ offense (797 runs) ranked fifth in the AL and Boston’s pitching (647 runs) third. The Yankees placed second in runs scored (851) and fifth in runs allowed (669), and as you might have heard, their 267 home runs set a major league record while their .249 batting average placed them eighth in the AL, leading to the complaint that they rely too much on the long ball.

Of six postseason battles so far, including the two wild-card games, the team that out-homered its opponent was 4-0 — twice, including the Yankees-Red Sox ALDS, the teams went deep the same amount — so that whole small-ball thing looks quite overstated. However, the Yankees’ sluggers didn’t slug enough against the Red Sox’s pitchers, who did a far better job of limiting damage than did their Yankees counterparts.

If the pitchers’ track records hold, this series will feature minimal bullpenning.

“I think it’s just better for the game,” said Chris Sale, the Red Sox’s Game 1 starting pitcher. “It’s kind of one of those things where you have this starter versus this starter against these lineups. Obviously we both have very good bullpens and big arms on either side. But this is more, I guess, the traditional way to play the game, and the way I like to play the game better, anyways.”

This series itself constitutes a rematch of last year’s ALDS, when the Astros rolled over the Red Sox in four games and, combined with the Yankees’ remarkable comeback against the Indians in the other ALDS, created the perception the Yankees had leapfrogged their rivals. Then both the Yankees and Red Sox changed managers and imported sluggers, and the decided advantages to Alex Cora over Aaron Boone and J.D. Martinez over Giancarlo Stanton go a long way in explaining where things stand.

The Astros, meanwhile, are trying to become the first repeat champions since the Yankees three-peated from 1998 through 2000, and their key addition is right-hander Gerrit Cole. The Yankees tried to acquire Cole last winter from Pittsburgh, but fell short to the ’Stros. Houston also sports a considerably superior and upgraded bullpen from 2017, when manager A.J. Hinch wound up using many of his starters to relieve.

“I thought we have the best team we could ever have [last year],” reigning AL Most Valuable Player Jose Altuve said. “And then we show up this year. And on paper, the team looks way better.”

Martinez admitted he thought the ALDS would go five games “because that’s how it’s been all year against [the Yankees].” Instead, the Sox won two straight at Yankee Stadium, prompting them to play “New York, New York” — a jab back at Aaron Judge for blasting it after the Yankees’ Game 2 victory at Fenway — as they partied in the visitors’ clubhouse.

If the Red Sox win this round, Martinez mused with a smile: “What’s their song, ‘Deep in the Heart of Texas?’ I don’t know. Probably not.”

Red Sox in 7. Yankees, either way, in agony.