The chairs are sliding more “feverishly” back and forth across the deck of the unsinkable National League Central as the Cubs and Cardinals open a series tied for the division lead for the first time since the 2017 season opener.

Three days after the Cubs picked off low-cost left-hander Derek Holland in a trade to help contain Brewers MVP hitter Christian Yelich and other pesky lefties, the Cardinals on Monday traded for lefty reliever Zac Rosscup to stash at Class AAA for possible future use against the lefty-averse Cubs.

Meanwhile, the Brewers — fresh off a series victory over the Cubs at Miller Park — traded for Pirates starter Jordan Lyles after watching three of their starters leave games with injuries in less than a week.

Could another Giants left-hander — such as Drew Pomeranz — be in play if the Cubs find the right price? And what will the Cardinals and Brewers be able to pull off?

Blockbusters be damned, less than two days remain before Wednesday afternoon’s trade deadline, and less than two months remain in the season with those three teams separated by a game atop the division, all at about an 86-win pace.

Don’t count on an MVP or Cy Young acquisition to suddenly shake up the division. And if you believe those in the clubhouse, don’t expect one team to suddenly run away from the rest.

But while the NL Central won’t challenge for baseball’s sexiest division this year, this week’s Cubs-Cards series may well challenge Kris Bryant’s St. Louis-is-boring theory as they open the most critical series they’ll play this year (at least until the next time).

“It’s no secret that the division’s gotten better. Everyone’s gotten better,” said Cubs left fielder Kyle Schwarber, who was coming off a two-homer, seven-RBI game Sunday in Milwaukee. “But we’re a really good team. When we’re playing our baseball, it’s hard to beat us.”

But what exactly is “our baseball” when it comes to the Cubs this year? Are the other teams really that much better? Are the Cubs not as good, not as complete as they have been in recent seasons?

They’re about to find out, maybe quickly, with these storylines in play:

Did somebody say blockbuster?

The Cubs and Cardinals made their signature moves well ahead of the trade deadline, and both Paul Goldschmidt (Cardinals) and Craig Kimbrel (Cubs) are worth watching for their impact on this series and the promise of their impact down the stretch.

Goldschmidt, the six-time All-Star first baseman acquired from the Diamondbacks over the winter, is one of the hottest hitters in the game and was named the NL’s Player of the Week on Monday after a week that included six consecutive games with homers.

Kimbrel, the $43 million closer who was signed in June and added to the Cubs’ roster this month, is a seven-time All-Star who has not pitched like it so far, showing inconsistent velocity and command, most recently allowing two home runs in the 10th inning Saturday to blow the save in a walk-off loss to the Brewers.

Sweep stakes

The home team has swept all three previous Cubs-Cardinals series this year, with much more at stake this time — especially for the Cubs, who haven’t won a road series since the middle of May.

Since May 1, the Cubs haven’t trailed in the division by more than 2½ games; they haven’t led at any point this season by more than 2½. The Cardinals haven’t led by more than three games all year and haven’t trailed by more than three since July 2.

A sweep by either team could amount to a tectonic shift in this division.

Left-handed complement?

The Cubs are the second-worst-hitting team against left-handers in the league, which helps explain some of their struggles during a road trip in which they lost both games started by opposing lefties and struggled late against lefty relievers such as Pomeranz, Will Smith, Josh Hader and Alex Claudio.

“If there was one thing I would have thought for sure at the beginning of the year, it’s that we would thrive against left-handed pitching and lefty starters,” team president Theo Epstein said.

The Cardinals don’t have any left-handed starters and scant few lefty relievers. But old World Series foe Andrew Miller bears watching this week. He’s rested and has been pitching well for two months — in particular over his last 15 appearances (1.69 ERA, 15 strikeouts, three walks).

Road hazards

The Cubs have the second-worst road record in the NL (better than only the Mets) and have lost 20 of their last 28 road games — including four of six through the first two cities of this three-city trip.

They haven’t won a game in St. Louis in a year and a day as they take the field Tuesday.

“I’ve never seen anything like this,” reliever Steve Cishek said.

“It’s been bipolar,” manager Joe Maddon said. “And I don’t have any solid explanation. The methods are the same. The guys are the same. Everything’s the same.

“Is it because other teams are better at home? I don’t know. It’s been difficult to wrap our mind around because we know we’re better than that, but we haven’t been.”