The 2021 MLB season is fast approaching, and because there will be no expanded postseason this year, playoff spots will be at a premium. Three division winners and two wild card teams in each league, and that's it. The current postseason format creates a significant incentive to win the division. With that in mind, we're going to preview each division race and break down the potential X-factors between now and Opening Day. Today, we'll be highlighting the National League East.

For two seasons now, the NL East has been expected to be a powerhouse, but the division hasn't quite lived up to its hype just yet. Sure the division is stacked with Cy Young and MVP candidates from nearly every club, and the last four of five NL Cy Young winners and three of six NL MVP winners were from this division. But, the division itself hasn't been able boast a whole lot of parity lately.

The Atlanta Braves have dominated, taking the NL East crown three years in a row. Even when the Washington Nationals won the World Series in 2019, they suffered from a serious championship hangover during the abbreviated 2020 season. Could this division race prove to be tighter than any other in baseball in 2021? For now, the Mets and Braves seem to be the favorites, but can the Phillies or Nationals rebound? Can the Marlins make things even more interesting by taking another step forward in their rebuild after their surprise playoff run last year? One thing we know for sure is that the race for the NL East crown is going to be a fun one.

Now, here is one 2021 X-factor for each NL East club, listed alphabetically.

Atlanta Braves: Health of Soroka (and his rotation mates)

In 2020, the Atlanta Braves took home their third straight National League East title but fell short again of reaching the World Series. The Braves held a 3-1 lead in the National League Championship Series, but the Los Angeles Dodgers won Games 5, 6, and 7 to surge past them. Prior to their deep playoff run last season, the Braves had not advanced past the NLDS round since 2001. So, after nine postseason trips without ever reaching the NLCS, their long-awaited return ended in heartbreak. The Braves have not been to the Fall Classic since 1999. For a team as talented as the Braves, the last few seasons have got to feel disappointing. The ultimate goal is winning the World Series, and despite their balanced roster of veterans and an impressive young core, they're still left short of a championship. The club's now reached the point where they'll have to separate themselves from being another October disappointment to being a World Series champion.

During the 60-game sprint of a season last year, the Braves overcame the seemingly constant injury setbacks their pitching staff took. In 2021, we're back to a full 162-game season and Atlanta isn't going to be able to get by if its rotation is hit with another barrage of injuries. Atlanta has a stacked lineup and I don't foresee any major issues with the reigning NL MVP Freddie Freeman,  2018 Rookie of the Year Ronald Acuna Jr. and a returning NL home run leader Marcell Ozuna. For these division champs, the health of their rotation will be of utmost importance to their success in 2021. Let's take a look at the projected rotation:

1. RHP Mike Soroka (recovering from a ruptured Achilles tendon)
2. LHP Max Fried (finished fourth in NL Cy Young voting) 
3. RHP Charlie Morton (signed to a one-year, $15 million deal)
4. RHP Ian Anderson (impressed in his rookie campaign) 
5. LHP Drew Smyly (signed to a one-year, $11 million deal) or RHP Kyle Wright (5.32 ERA, 92 ERA+ in 38 IP in 2020)

Adding Morton gives Atlanta a steady veteran presence at the front end behind Soroka and Fried. The addition of Smyly should help to regain rotation depth as well, with some of the club's other internal options at this point including Touki Toussaint, Sean Newcomb, Bryse Wilson and Huascar Ynoa. Soroka still doesn't have a timetable to return to the starting rotation, but he's made good progress in his recovery so far and threw two innings in a simulated game earlier this month. A healthy (and productive) return from Soroka along with season long health for the rest of the starters will help this club go after the Commissioner's Trophy.

Miami Marlins: Young staff vs. full season

The 2020 Miami Marlins surprised the baseball world with their unexpected postseason run to the National League Division Series. t was truly one of the more wild Cinderella stories to come out of the shortened season. But the Marlins had a minus-41 run differential, the seventh-worst in the league. 

I don't see anything like the 2020 run repeating itself in a full, 162-game season. Instead, in 2021, the biggest X-factor for Miami is going to their young players taking the next step forward, making sure they're improving and helping the club begin its transition from rebuilder to contender. They're still probably two or three years out from actually being competitive, especially considering they're up against some really tough teams in their division.

The good news is that coming off their surprise playoff run, this team has some reason for excitement; the future is bright. In the club's rotation, it's Sandy Alcantara, Pablo Lopez, Trevor Rogers, Elieser Hernandez and Sixto Sanchez headlining a young but talented staff. Every starter is 25-years-old and younger. The talent and promise is there for this club's young core, but the 2021 season will be the true test to see how each fares over the course of a full season.

New York Mets: Thor's return and rotation behind deGrom

Under new owner and billionaire Steve Cohen, the Mets' busy offseason was enough for most of us here at CBS Sports to call them the division favorites. And also like the Braves, the Mets are going to have to rely on their rotation's success in 2021. New York has a few concerns ahead of the 2021 season: extensions for Francisco Lindor, Michael Conforto and how they'll handle their outfield now that there's no universal DH. The offense looks good (even with the loss of Robinson Cano due to second PED suspension), in fact, it may turn out to rebound from a sluggish 2020 this year. But their biggest X factor is going to be the success of their rotation behind Jacob deGrom.

Marcus Stroman is returning after opting out of the 2020 season, while the Mets also addd Carlos Carrasco and Taijuan Walker. For right now, here's a look at what the rotation will look like in Queens:

1. LHP Jacob deGrom, 32-years-old (finished third in NL Cy Young voting)
2. RHP Marcus Stroman, 29-years-old (opted out of 2020 season)
3. RHP Carlos Carrasco, 33-years-old (acquired in Lindor trade)
4. RHP Taijuan Walker, 28-years-old (signed a two-year, $20 million deal)
5. LHP David Peterson, 25-years-old (3.44 ERA, 123 ERA+ in 49 2/3 IP during rookie season) or LHP Joey Lucchesi, 27-years-old (coming off a disappointing 2020 season)

On paper, this looks good. Plus, Noah Syndergaard is set to return from his Tommy John surgery sometime this summer. The Mets are going to need deGrom to be deGrom again, Stroman, Carrasco and Walker hold down the middle of the rotation with solid starts, and improvements from Peterson and/or Lucchesi in the No. 5 spot. Syndergaard is the biggest unknown here and could make a huge impact if he's close to his usual hard-throwing self when he returns.

Philadelphia Phillies: How improved is bullpen?

Remember when the Phillies made a record-breaking (at the time) free agent deal for Bryce Harper? That literally feels like ages ago. It was only just this time, two years ago. Since then, the Phillies have stumbled their way to back-to-back third-place finishes in the NL East. It's playoffs or bust for Philly in 2021. They're a competitive ball club with well-known players, and their front office (now led by Dave Dombrowski) did go out and make some improvements this winter.

For the Phillies' biggest X-factor in 2021, we're going to be focusing on the bullpen. In case you need a refresher, the Phillies bullpen last year was absolutely atrocious. I'll just quickly run through some stats. Phillies relievers combined for a historically bad ERA of 7.06 over 189 appearances. That counted for the second-worst bullpen ERA in MLB history. In 186 innings, the bullpen gave up 246 hits, 159 runs (146 earned), 87 walks, and 42 home runs. There were more blown saves (12) than successful saves (11) last season. 

Luckily for Phillies fans, the club did actually go out and improve the bullpen this winter. The biggest of which included signing free-agent reliever Archie Bradley to go along with a few tweaks with the additions of Jose AlvaradoBrandon Kintzler and Tony Watson. The Phillies will need contributions from a consistent set of arms out of the pen if they hope to avoid another crash-and-burn season. Other than that, Philadelphia will mostly be running back to same team from last year with J.T. Realmuto and Didi Gregorius returning to go along with Harper, Rhys Hoskins, Andrew McCutchen and the rest of the gang.

Washington Nationals: Will big-name SPs bounce back?

The 2019 champions are coming off a disappointing fourth-place finish. This year's going to be the moment that truly dictates which direction the Washington Nationals are heading in. For the Nats, the health and performance of their pitching staff is going to be the most notable X-factor in 2021. Last season, Washington's rotation issues figured to be the biggest roadblock in returning to the postseason. Stephen Strasburg was shut down after two ineffective starts and later underwent season-ending surgery for carpal tunnel syndrome. It's not what you want. Especially after signing Strasburg, the 2019 World Series MVP, to a seven-year, $245 million deal the offseason prior. Max Scherzer battled nagging injuries throughout the shortened season and finished with a 3.74 ERA in 12 starts, his highest mark in eight seasons, and a 4.00 strikeout/walk rate after he led the NL at that stat for the two prior seasons. In his second year with the Nats, Patrick Corbin trended in the wrong direction with a 4.66 ERA (99 ERA+) in 11 games. Beyond that, Anibal Sanchez and Austin Voth struggled as well.

All that's not to say that the three-headed monster of Scherzer, Strasburg, and Corbin is over. It's just to say that this club will desperately need a bounce-back year from the entire trio in 2021. It's also a good point to make note that pitchers overall struggled significantly in 2020. The quick build-up in a short season, lack of a normal spring training and all of the unexpected delays and start-stops due to COVID-19; all of that factored in for pitchers in MLB's bizarre 2020 season. 

What will likely help add some support after the top three is the addition of veteran starter and five-time All-Star Jon Lester. The Nationals signed Lester to a one-year deal in January and he'll be able to step in as the innings-eating No. 4 starter in his age-37 season. If Scherzer, Strasburg and Corbin can return to form in 2021, with Lester stepping in as a solid fourth starter, then the Nationals will already be in much better shape than they were in 2020.