The Post’s Mark W. Sanchez previews the NL Central.

O/U wins: 89.5

Key player: Christian Yelich. For the first time in his career, he played like an average major leaguer last season, and neither he nor the team knows what happened. He averaged 40 home runs with a .327 batting average in his first two Milwaukee seasons, and in a lineup with questions, the outfielder’s return to form would answer a big one.

Player who’ll need to step up: Eric Lauer. Brandon Woodruff broke through as a Brewers starter in 2019; Corbin Burnes in 2020; both Adrian Houser and Freddy Peralta made the leap last season. The left-hander Lauer, a former first-round pick, is up next after he was excellent in last season’s second half.

Name you’ll get to know: Aaron Ashby. The 23-year-old southpaw debuted last season, mostly in relief, but the Brewers see the former first-rounder as a starter with a high ceiling. He’ll need to hone his command.

Biggest question mark: Can Milwaukee unlock its top hitters? Impact bats such as Yelich, Keston Hiura and Lorenzo Cain have disappointed. The talent is there, especially with full seasons of Willy Adames and Rowdy Tellez and the additions of Andrew McCutchen and Hunter Renfroe.

How it’ll go down: The reigning division champs return what might be the best and deepest rotation in baseball. The lineup has questions that McCutchen can help answer, but the Brewers should have enough arms — in the bullpen, too, which projects as a major strength behind Josh Hader and Devin Williams — to hold off challengers.

O/U wins: 84.5

Key player: Steven Matz. With shoulder issues surrounding ace Jack Flaherty, there is a hole at the top of the rotation that Matz could help fill. The former Met revived his career in Toronto last season and pitched to a 3.82 ERA. Will that number look even better outside the AL East — and with five defenders behind him who won Gold Gloves last season?

Player who’ll need to step up: Paul DeJong. The Cardinals did not upgrade at shortstop despite DeJong batting .197 last season and temporarily losing his job to Edmundo Sosa. DeJong hit 30 homers and was an All-Star as recently as 2019, and the Cardinals are counting on a rebound.

Name you’ll get to know: Nolan Gorman. The Cardinals have begun moving around the natural third baseman, who played some second last season because Nolan Arenado has the hot corner covered. The strong 21-year-old lefty hitter, who knocked 25 minor league homers last season, will be up at some point.

Biggest question mark: The Cardinals surprisingly fired Mike Shildt, a largely successful manager, after a 90-win season. Is Oliver Marmol able to get more out of this veteran club?

How it’ll go down: The old core — Albert Pujols, Yadier Molina and Adam Wainwright — will be working with the new core of Arenado and Paul Goldschmidt. St. Louis fans will enjoy this season, even if the Cardinals don’t have the pitching that Milwaukee has.

O/U wins: 75.5

Key player: Willson Contreras. Anthony Rizzo, Kris Bryant and Javier Baez are gone, and Contreras could be next, as his name repeatedly has surfaced in trade rumors. But the catcher is still in Chicago and is the most proven piece among the position players. He has been solid the past two seasons despite a step down from his 2019 form, and a return to his All-Star ways would help his value to the team and on the trade market.

Player who’ll need to step up: Kyle Hendricks. The eight-year standout never registered an ERA above 3.95 until last season, when it ballooned to 4.77 amid a brutal second half. If he’s right, the righty could form a potent duo with Marcus Stroman atop the rotation.

Name you’ll get to know: Seiya Suzuki. Say hi to Seiya. The Cubs won the bidding for the 27-year-old Japanese outfielder, who is regarded as a five-tool talent and hit 38 homers in the Japan Central League last season.

Biggest question mark: Starting pitching depth. Behind Hendricks, Stroman and Wade Miley are oft-injured Drew Smyly and several unproven options, such as Alec Mills, Adbert Alzolay, Justin Steele and Keegan Thompson.

How it’ll go down: The Cubs of recent vintage are gone, but there is enough talent and high-upside gambles — including former Yankee outfielder Clint Frazier — to make them interesting all season.

O/U wins: 74.5

Key player: Jonathan India. As the Reds have torn down, their Rookie of the Year second baseman becomes even more important. Can he make the jump to an All-Star after posting an .835 OPS last season?

Player who’ll need to step up: Mike Moustakas. His first two seasons in Cincinnati since signing a four-year, $64 million contract have been disastrous. A heel injury limited the infielder to 62 games last season. At 33, he will try to prove he has more in the tank.

Name you’ll get to know: Hunter Greene. You may already know the name because of the 2017 Sports Illustrated cover that called him the “star that baseball needs.” After Tommy John surgery, rehab and minor league time, the 22-year-old fireballer who has touched 104 mph looks ready and is expected to begin the season in the rotation.

Biggest question mark: Starting pitching. Trades have depleted the group, which now needs strength and health from Luis Castillo, Tyler Mahle and Mike Minor. There are significant questions beyond the front of their staff.

How it’ll go down: The Reds won 83 games last season, edging over .500, and then blew it up this offseason. Nick Castellanos, Sonny Gray, Wade Miley, Jesse Winker, Amir Garrett, Eugenio Suarez and Tucker Barnhart are gone, and many wins are likely gone with them.

O/U wins: 65.5

Key player: Ke’Bryan Hayes. The third baseman looked like a piece to build around in 2020, when he caught fire for 24 games and received Rookie of the Year votes. Last season was marred by injuries to both hands and his left wrist. Pittsburgh needs offensive help around outfielder Bryan Reynolds.

Player who’ll need to step up: Mitch Keller. The one-time top prospect has yet to pan out and lugged around a 6.17 ERA through 23 starts last season. But his velocity has been up through a good spring, and there’s hope his fourth season will be the charm.

Name you’ll get to know: Oneil Cruz. You’ll get to know the 23-year-old but not right away, as Pittsburgh is opting to start the season with its top shortstop prospect in the minors. The 6-foot-7 lefty hitter with good speed and power will be in the majors before long.

Biggest question mark: The Pirates have finished last in the division three years straight, and Max Scherzer is out-earning their entire roster this season. At what point does Pittsburgh even attempt to be competitive?

How it’ll go down: Pittsburgh lost 101 games last season, which actually represented a nice uptick in win percentage from their 19-41 2020 campaign. They did little to improve this offseason, so progress from prospects is all that will matter.