When you start compiling a shortlist of MLS Cup contenders, the teams that easily come to mind are FC Dallas and the New York Red Bulls, who lead the Western and Eastern Conferences, respectively.

Maybe you're drawn to the Colorado Rapids' worst-to-first story and the club's grind-it-out defensive mindset. Some will talk about star-studded Toronto FC and a second-year New York City FC club led by David Villa, Andrea Pirlo and Frank Lampard. 

You can't count out Bruce Arena and the LA Galaxy either anytime the postseason rolls around, especially with the star power they can trot out on to the pitch any given week combined with the former United States head coach's managerial genius.

But there's one other team you should add to the mix among the perennial favorites and top teams from the 2016 regular season. 

They definitely aren't the sexy pick to be crowned champions on December 10, but D.C. United are a team to look at as a serious MLS Cup contender. 

Under the guidance of manager Ben Olsen, D.C. have put together a six-game unbeaten run and have lost just once since July 31. 

The Black and Red were left for dead along with the Columbus Crew and Chicago Fire, who both still sit at the basement of the Eastern Conference, as the calendar flipped from July to August. But a few changes have been made to boost them to the cusp of a hosting a match in the knockout round of the postseason. 

United enter the final day of the regular season—Decision Day as it's being called by the league—in fourth place in the Eastern Conference. All it takes to lock up at least a home match at RFK Stadium is a win over Orlando City on Sunday at Camping World Stadium. 

All of this has been made possible by a pair of shrewd acquisitions near the end of the summer transfer window—one of which was a deal with D.C.'s biggest rival—a stout defense and a manager who has made the required tweaks to his side.

Let's start with the trades for Patrick Mullins and Lloyd Sam because both of the attack-minded midfielders have brought a new dimension to the final third, and they've actually made D.C. an attractive team to watch, which is a big step considering what they've looked like in past years. 

The addition of Mullins, a 24-year-old striker in his third Major League Soccer season, has meant the world to D.C. The University of Maryland product didn't receive a chance to blossom into the striker he should be under Patrick Vieira at New York City FC this season. 

With playing time diminishing and D.C. in desperate need of a consistent scorer, Olsen pulled the trigger on one of the best moves of the season. Since joining D.C. on July 20, the No. 11 pick in the 2014 MLS SuperDraft has scored eight goals in 12 matches. 

Mullins is second on the team in scoring behind Lamar Neagle, who was brought in during the offseason from Seattle. The lively presence of Mullins in front of net has been a welcome sight to the eyes of D.C. fans after Alvaro Saborio and Fabian Espindola failed to provide a consistent spark up top during the first half of the campaign.

Saborio remains a solid option off the bench for the Black and Red, especially in the postseason with his wealth of experience. Espindola was jettisoned to Vancouver to make room for Mullins on the roster. Kennedy Igboananike, who was brought in from Chicago at midseason, is also available off the bench.

The rest of the goals have come from a wide variety of players, but Mullins has ushered himself in as the top scorer for years to come in the nation's capital, and given his newfound confidence in the box, D.C. have a chance to pounce at any second. 

Acquiring winger Lloyd Sam from the New York Red Bulls has also been beneficial to the attacking style of United. The 32-year-old, who featured in plenty of big matches with the Red Bulls, put in one of his best performances of the season a week ago as he contributed to two goals in D.C.'s playoff-clinching win over NYCFC. 

Mullins and Sam have taken some of the attention away from Argentine playmaker Luciano Acosta, who was the club's top attacking target for the first five months of the season.

Since opposing defenses can't key in on one player now, Acosta will have more space moving forward, especially when the back-and-forth postseason affairs begin. 

And then there's Neagle, who emerged as a super-sub in August and September with two goals and two assists. The former Seattle man also added three goals as a starter, including a brace against Toronto on October 2. 

The D.C. defense has complemented the offensive firepower and even added to it at points during the recent spell of good form. 

The defensive line led by center-back pairing Bobby Boswell and Steve Birnbaum has conceded three goals in the last four matches, all of which have been victories. That number is much better than the 15 strikes let in from July 31 to September 16 when the team was hitting its stride. 

Goalkeeper Bill Hamid has kept the club in quite a few games during the course of the regular season, but he can't do it all if the Black and Red want to make it to the MLS Cup, although the United States international might be able to achieve the task if he tried. 

D.C.'s path to the MLS Cup could end up being an easy one if they continue to play like they have over the last month. Most of the playoff teams in the Eastern Conference have shown signs of weakness that can be exploited by the right game plan, which is where Olsen's managerial experience comes into play. 

The former United States international led the Black and Red to the Eastern Conference semifinal in 2012 and 2015 and helped the club rebound from an atrocious 2013 to earn a playoff berth the next year. 

Olsen has also done a great job working with his squad this season given the long-term injury issues the Black and Red have faced.

Midfielder Chris Rolfe, who was the club's top player a year ago, has been out with a concussion, while defenders Chris Korb and Kofi Opare are both out with injuries. The D.C. coach has also had to deal with the absence of central midfielder Marcelo Sarvas and full-back Sean Franklin in recent weeks. 

In any other season, Olsen would've been in the running for MLS Coach of the Year, but Pablo Mastroeni in Colorado, FC Dallas' Oscar Pareja and Vieira are the favorites to receive that honor. 

Regardless of who D.C. ends up playing in the knockout-round match, they should have an upper hand on either Montreal or Philadelphia.

The Impact have had a good amount of ups and downs this season, and the Didier Drogba drama from the last week doesn't exactly help a team's focus on the postseason. Montreal's attack has plenty of weapons—with or without the former Chelsea man—but their defense is a bit concerning as they've recorded just three clean sheets since the start of July.

The easier matchup for D.C. would be the struggling Union, who backed their way into a playoff berth on the penultimate Sunday of the regular season. No matter how awful D.C. play in that match, they should win due to the lack of preparedness and effort in the Philadelphia squad. 

When it comes to the semifinal and final rounds, United face a solid chance of advancing against either Toronto or NYCFC, who both still have questions in defense despite the stellar attackers in each lineup.

The biggest matchup problem for the Black and Red, or any team in the East if we're being honest, is the Red Bulls and their trademark pressing system. The good news for United is they've earned five points from three matches against their top rival in 2016, including a pair of come-from-behind 2-2 draws. 

D.C. may not have a chance to challenge the Red Bulls for a 180-minute series if they settle in and defend against Bradley Wright-Phillips, Sacha Kljestan and Co., but they do have the capability to strike early and find vulnerabilities in the press. 

Anything is possible when it comes to the MLS Cup, which will most likely be played at a Western Conference venue if D.C. come out of the East. The road environment shouldn't hurt United's blueprint for success by that point in the season. 

The MLS Cup final may still be a month and a half away, but if you're looking for a dark-horse contender to get behind, hopping on the D.C. bandwagon right now is for you. 

Joe Tansey covers MLS for Bleacher Report. You can follow him on Twitter, @JTansey90.

All statistics obtained from MLSSoccer.com. 

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