This is the fourth year of MLB’s one-game wild-card format, and for anyone who has attended one of these games, the question could well be: What took so long? This change in the postseason qualification formula not only returned emphasis to winning the division – the only way a team can guarantee itself a full series – but also essentially starts October with a pair of Game Sevens.

A look at the American League version.

Houston Astros (86-76) at New York Yankees (87-75)

Tuesday, 8:08 p.m., Yankee Stadium, New York

Season series: Yankees 4, Astros 3

Where they rank in the American League:

Runs scored: Yankees second (4.7/game); Astros fifth (4.5/game)

OPS: Yankees fourth (.744); Astros second (.752)

ERA: Yankees eighth (4.05); Astros first (3.57)

Astros starter: Dallas Keuchel (20-8, 2.48 ERA)

Given what the Astros went through to get here – playing 162 meaningful games before they locked up the second wild-card spot Sunday – they’re incredibly fortunate to have their ace lined up, on regular rest, for their first postseason appearance since 2005. Keuchel, a seventh-round draft pick out of Arkansas in 2009, broke out this season, leading the league in innings pitched (232), walks-and-hits per inning pitched (1.017) and wins – and, had he allowed just two fewer earned runs, would have beaten out David Price for the ERA title. (As it is, he lost by .03 of a run.) He’s not overpowering, but instead relies on an incredible slider-changeup-fastball mix to limit opponents to a .217 batting average.

Key matchup: Carlos Beltran

This is the 38-year-old switch hitter’s fifth trip to the postseason, in which he has a remarkable .333 average/.445 on-base percentage/.683 slugging percentage with 16 homers in 51 career games. No Yankee has a ton of experience against Keuchel, but Beltran has found success: 4 for 9 with a walk, a double and a homer.

Yankees starter: Masahiro Tanaka (12-7, 3.51 ERA)

Tanaka has pitched only once since Sept. 18 because of a strained hamstring he suffered while breaking out of the batter’s box while laying down a bunt against the Mets. Add that to the strained forearm that cost him all of May, and the main question with the right-hander – in his second season since coming from Japan – is clearly health. When he pitches, he’s generally good: He held hitters to a .221 average this year, and allowed three or fewer earned runs in 17 of his 24 starts. One Yankee concern: the long ball. Tanaka gave up 25 homers in 154 innings, an average of 1.46 per nine innings – the fourth-highest rate in the American League.

Key matchup: Carlos Correa

We don’t say this because, in their only matchup thus far, Correa went 2 for 3 with a two-run homer off Tanaka. We say this because Correa is the Astros’ most dynamic player. The rookie shortstop, who turned 21 last month, ripped 22 homers and 22 doubles in 432 plate appearances after being called up in early June. Should Houston win this game, Correa has a chance to become a household name by the end of the month.

Astros’ key late-game matchup: Will Harris vs. Alex Rodriguez

The right-hander, scooped up off waivers from Arizona in the offseason, has become manager A.J. Hinch’s main setup man for closer Luke Gregerson, and he allowed opposing hitters just a .168 average. He has never faced the right-handed-hitting A-Rod, who appears in the postseason for the first time since 2012, when his bat was so slow Manager Joe Girardi benched him against right-handers. In this comeback season, at age 40, Rodriguez slugged 23 of his 33 homers against right-handed pitching. As we enter the playoffs, he’s astonishingly a threat again.

Yankees’ key late-game matchup: Dellin Betances vs. Evan Gattis

Betances is in the conversation, with Kansas City’s Wade Davis, as the AL’s best reliever – and he merely sets up closer Andrew Miller. Consider, though, that he held hitters to a .157 batting average and .244 slugging percentage, with 131 strikeouts in 84 innings (!!!!!), and that status is inarguable. Gattis is the Astros’ best pure power threat, and 20 of his 27 homers came against right-handed pitching. The outcome of this matchup would favor the homer or the strikeout – and in a close game would be appointment television.