These are the 10 biggest pennant race X-factors

Less than five weeks to go. Five races to decide.

The American League Central, AL Wild Card, National League Central, NL Wild Card and NL East are all somewhere south of settled in the home stretch of the 2019 regular season. These are the 10 biggest X-factors that will determine the outcomes of those battles.

Can the Cardinals' young arms keep this up?

While an offensive upswing is obviously a reason for the St. Louis surge, the lineup was loaded with underperforming parts that have now more reasonably approximated their projected performance.

It's the pitching, which went from allowing 4.44 runs per game before the break to 3.55 after, that has been the bigger revelation. Maintaining this level of run suppression will likely require more of the same from 23-year-old Jack Flaherty (0.98 ERA in the second half) and 24-year-old Dakota Hudson (zero runs allowed in his last 18 2/3 innings) in the rotation. The 25-year-old Ryan Helsley has also provided a nice bullpen boost since a recent recall from Triple-A.

Will Rhys Hoskins get hot?

The consistency of the Phillies' offense has been so far south of expectations that the club took the rare step of replacing its hitting coach in mid-August. Hoskins has been the most vexing member of this bunch. Hoskins is a streaky hitter to begin with, but he hit .120/.315/.229 in August before a much-needed 2-for-4 (with a triple) against Pittsburgh on Wednesday.

The Phillies have a variety of roster issues, but they desperately need Hoskins to catch fire if they're going to assert themselves in this crowded NL Wild Card race.

What will the Indians get from Corey Kluber and Carlos Carrasco?

There's no getting around the fact that the projected output of the lineup took a huge hit when the Indians lost the hot-hitting José Ramírez to a broken hamate bone.

That makes the potential returns of Carrasco and Kluber to a pitching staff that has relied heavily on the young arms of Shane Bieber, Zach Plesac and Aaron Civale all the more important. Carrasco, who underwent treatment for leukemia this summer, will be used out of the bullpen when rosters expand. Kluber's status was still uncertain as of this writing, with an oblique injury delaying his return after he had essentially finished rehabbing a broken forearm and the clock ticking.

What do Jon Lester and Cole Hamels have left in the tank?

They are the highly respected, highly decorated, highly successful veteran leaders of this Cubs pitching staff. They are also both 35 years old and have a combined 6.51 ERA in the second half.

Glaring as that overall number is, both have sprinkled in some encouraging outings along the way, and Hamels' ERA is inflated by one particularly brutal bashing in Philadelphia in the small sample of opportunity since he came back from an oblique injury. But with seven games left against the Cardinals and a season of road struggles ending with a six-game trip, the Cubs need this prominent pair at its best for the home stretch.

What will the Rays get from Tyler Glasnow and Blake Snell?

The Yankees grab the headlines, but for the small-market Rays to be in contention despite losing more than 11 projected Wins Above Replacement overall (the most in MLB, per the data at mangameslost.com) is amazing.

That said, the injuries have caught up to this club lately. And because Brandon Lowe and Yandy Díaz are out for the remainder of the regular season, it falls on the pitching staff all the more to seal an AL Wild Card spot. Glasnow has been out since mid-May with a forearm issue, and Snell, the reigning AL Cy Young Award winner, had arthroscopic surgery in late July. The Rays, who have the Dodgers, Yankees and Red Sox on the schedule in the season's last two weeks, hope to get both back in mid-to-late September.

Can a bullpen army save the Brewers?

Christian Yelich might have instructed a fan named Roxane to "relax" about his nude photo shoot for ESPN The Magazine, but Brewers fans have every right to be frantic about dropping a series to the Cardinals to start a make-or-break stretch in which the Brew Crew will play 12 of its next 16 against the Cubs, Astros and Cards.

Because Milwaukee did not meaningfully address its rotation at the Trade Deadline, this club is likely to take full advantage of the last year of truly bloated September rosters and go bullpen-heavy in a bid to piece together effective pitching. The Brewers' total staff has an ERA north of 5 going back to the start of July.

Will young guns help the Twins nail down the AL Central?

While the bats are bashing at a historic pace, there are questions about the pitching staff, with 25-year-old José Berríos having posted an 8.44 ERA in August, and the bullpen (like just about every bullpen this year) showing inconsistency.

With six games remaining against the second-place Indians, getting Berrios on track is essential, and it will be interesting to see if the bullpen gets a boost from hard-throwing right-handers Brusdar Graterol (their No. 3 prospect, per MLB Pipeline) and Jorge Alcala (No. 23) when rosters expand.

A healthy Byron Buxton, who had a setback in his recovery from a left shoulder injury, is also a clear key here.

Will Sean Doolittle bounce back?

Certainly the Nats need Max Scherzer to finish with a flourish, especially if they're going to have any chance of actually advancing in October. But first they have to get there, and that means nailing down -- at the very least -- their current position atop the NL Wild Card pecking order and nailing down leads in general.

The latter objective has been a well-documented struggle for Washington this season (5.89 relief ERA), but Deadline acquisitions Daniel Hudson and Hunter Strickland have helped, and further reinforcement could arrive with the pending return of Doolittle from a knee issue. Doolittle has been a mess in the second half (7.36 ERA, 1.052 opponents' OPS), but the Nats are committed to him as their closer for now. He'll be particularly pivotal the first two weekends of September, when the Nats have their last, best shot at running down the Braves.

How will the A's juggle their pitching depth?

Oakland's surprising rotation, which survived the loss of breakout right-hander Frankie Montas (PED suspension) in part because of the acquisitions of Tanner Roark and Homer Bailey, has keyed the seemingly annual A's surge. A roster crunch is coming with Sean Manaea nearing a return from shoulder surgery, top prospect Jesus Luzardo a potential September option and a decision needing to be made about Matt Harvey, who has an out in his Minor League pact Thursday.

Will any of the above options land in the erratic bullpen, a la prospect A.J. Puk?

The A's have the most favorable remaining schedule of the AL Wild Card contenders (Rays and Indians), and Oakland Coliseum would be a tough place to play a winner-take-all tilt.

Will Brandon Nimmo, Robinson Canó and Jed Lowrie give the Mets a jolt?

Winning 20 times in a 25-game stretch is exhilarating, exciting, and, yes, exhausting. The Mets went on that mesmerizing run despite an array of injuries that weakened their bench, and that meant riding guys like Pete Alonso, Michael Conforto, Amed Rosario and Wilson Ramos particularly hard.

Getting utility man Jeff McNeil back earlier this week was essential, and Nimmo is close behind. Cano, whose torn left hamstring on Aug. 4 looked like a potential season-ender, is already taking batting practice and could be ready sometime in September. Lowrie has yet to play this year, as he started the season on the injured list with a left knee capsule sprain and is currently on a rehab assignment.

The Mets have looked gassed at times in recent days, so the roster reinforcements will be welcomed.