Alarm bells are sounding as Cubs' early-season strength quickly becomes a weakness

At 35-22, the Chicago Cubs are flying high, in first place in the National League Central - despite opening the regular season with the toughest strength of schedule any team faces in a single month this year.

The Cubs are 17-9 in May, and it's no mystery why. The offense has been otherworldly, with two of the top offensive players in the league driving in runs at a jaw-dropping clip in Pete Crow-Armstrong and Seiya Suzuki. Rookie Matt Shaw has returned from Iowa looking like a completely different player at the plate, not to mention turning in some highlight-reel-caliber defense at third base.

Thankfully, the club is clicking at the plate - because what ranked as one of the best starting rotations in Major League Baseball in April has gone sideways without Shota Imanaga. Since May 5, Cubs starters rank 27th in baseball with a 5.06 ERA.

Two key cogs in Cubs' rotation have been ineffective in their recent starts

The two biggest culprits are Friday's losing pitcher, Colin Rea, and right-hander Ben Brown. Cincinnati hit Rea hard in his latest start, tagging him for six earned on 10 hits - including three home runs - over 5 2/3 innings of work, raising his ERA on the year to 3.96. That seems palatable for a guy of his pedigree, but it's jumped rapidly from 1.46 after his first start of May to nearly 4.00 heading into June.

He was never going to drop a sub-2.00 ERA over the course of 162 games. But he allowed six runs in each of his last two outings (both against the Reds) - and hasn't been as sharp, especially with his fastball. The Cubs don't need him to pitch like an All-Star, but he can't be giving up a half-dozen runs every time he's out there, either.

Brown seems like the bigger concern because, of the two, he has the higher ceiling and greater potential to step up and pitch like a top-of-the-rotation arm. That's not what's happened of late, though, and the Cubs are open to anything to get him right, including starting Saturday's game with an opener rather than Brown.

Over the last 30 days, Brown has a 6.75 ERA in five starts and opponents are hitting nearly .280 against him during that span. He hasn't been sharp - and he knows it. With Imanaga not expected back until 'well into June' and Justin Steele out for the year, this rotation is hanging by a thread, with Matthew Boyd the main bringer of consistency of late.

Things will level off once Imanaga returns and Jed Hoyer works his summer magic, hopefully bringing in a top-shelf arm to add to the mix. But the numbers paint a worrisome tale - and the only reason more folks aren't in a full-blown panic is because the bats have helped cover up the rotation's recent shortcomings.