Since the advent of the wild card in 1995, an entire division has finished .500 or better just one time. It happened with the National League East in 2005, when the Braves won the division with a 90-72 record and the fifth-place Nationals were just nine games back at 81-81. Just six games separated the five teams entering September, so the final month began with a legitimate five-team race for the division title.

We could get a similar tightly packed chase in the NL East in 2021. While the projection systems place the Marlins a distant fifth in the division, you can't exactly ignore a team that finished ahead of the Phillies, Mets and Nationals and made the expanded postseason in 2020.

With the Nationals finally getting their season started Tuesday night against the Braves and the Phillies hosting the Mets on ESPN (7 p.m. ET), let's look at some of the key factors that will decide the division race.

1. Bullpens

Yes, we're going straight to the bullpens. The Phillies are the obvious team to mention here, coming off a 7.06 bullpen ERA that was the worst in the majors since the 1930 Phillies, but all five teams have potential issues.

Braves: The 2020 Atlanta bullpen did an excellent job covering for a rotation that struggled, but Mark Melancon, Shane Greene and Darren O'Day are gone after combining for a 2.29 ERA and just four home runs allowed in 66? innings. Will Smith takes over for Melancon as closer, and he had gopher ball problems last year, allowing seven home runs in 16 innings and then a big one in the playoffs to the Dodgers' Will Smith that turned the momentum in the NLCS.

Marlins: The Marlins had one of the oldest pens in the majors in 2020 and have to replace closer Brandon Kintzler, who signed with the Phillies. Anthony Bass, another vagabond veteran, is getting his first shot as closer, but he promptly blew a 4-2 lead on Opening Day.

Phillies: Dave Dombrowski has rebuilt the pen after last year's disaster, bringing in Kintzler, Archie Bradley, Jose Alvarado and Sam Coonrod. Homegrown Connor Brogdon could be an impact middle reliever and Vince Velasquez should be a full-time reliever, where his stuff should play up over short outings. As my ESPN colleague Tim Kurkjian pointed out, it's a group that throws very hard (other than the sidearmer Kintzler). After ranking 22nd in the majors in bullpen velocity in 2020, the Phillies ranked third after the first weekend of the season.

Mets: We saw very bad Edwin Diaz in 2019 (5.59 ERA) and very good Edwin Diaz in 2020 (1.75 ERA, 50 K's in 25? innings), but the bigger issue may be the setup guys, especially with Seth Lugo out after surgery to remove a bone spur. Free agent Trevor May should be the eighth inning guy, but veterans Dellin Betances and Jeurys Familia, who didn't exactly impress last season, looked shaky in spring training. Blowing a lead after Jacob deGrom pitches like, well, Jacob deGrom as the bullpen did on Monday night is exactly what the Mets can't afford to see happen this season.

Nationals: Even when they won the World Series in 2019, the bullpen was thin behind Sean Doolittle, and they basically used two relievers (Doolittle and Daniel Hudson) in key moments in the postseason, with the starters filling in. Doolittle is gone, with Brad Hand the new closer. Tanner Rainey has the best pure stuff and Hudson is still around. Will Harris begins the season on the IL, but should return shortly and will assume a key role.

2. Defense

Maybe the best way to track team defense is just to like at defensive efficiency -- the percentage of balls in play turned into outs. The inverse of that is batting average on balls in play. Here's where the NL East teams ranked among all 30 teams in 2020:

Braves: .294 (19th)
Marlins: .297 (22nd)
Mets: .316 (27th)
Nationals: .317 (28th)
Phillies: .343 (30th)

The Braves at least have a chance to be pretty good with Dansby Swanson, Cristian Pache and Ronald Acuna Jr., although they're faking it a bit in left field with Marcell Ozuna (who mostly was a designated hitter last season). The Marlins' three primary outfielders -- Starling Marte, Corey Dickerson and Adam Duvall -- have been good defenders in the past but are all also on the wrong side of 30. The Mets will be much better at shortstop with Francisco Lindor and catcher with James McCann (they've easily been the worst team throwing out base stealers the past two seasons with Wilson Ramos), but have potential problems in left field and third base, and Brandon Nimmo is a bit stretched in center field.

Note on the Mets' defense: SNY reporter Steve Gelbs told a good anecdote about Lindor's leadership. During a cutoff drill in spring training, after an outfielder missed the cutoff, Lindor stopped the drill and implored the team to do it right. Top of the first inning of the Mets' first game: Rhys Hoskins doubles to right-center, but is caught trying to stretch it into a triple with a perfect 8-4-5 relay.