Here's a viewer's guide to the MLS playoffs' conference final series.

Both series will be played over two legs, home and away, with away goals counting as the first tiebreaker. The first legs will be played on Sunday; the second legs will be played next Thursday.

Eastern Conference: 1. New York Red Bulls vs. 2. Atlanta United

First leg: Sunday, 5 p.m. at Mercedes-Benz Stadium, Atlanta (ESPN and ESPN Deportes, ESPN.com/Watch)
Second leg: Thursday, 7:30 p.m. at Red Bull Arena, Harrison, N.J. (Fox Sports 1, Fox Deportes, FoxSportsGo.com)

Three storylines

1. Atlanta's explosive offense vs. New York's stingy defense. It's simplistic to say, because New York's attack and Atlanta's defense both have some bite. But it's true, and impossible to ignore. Atlanta scored a league-high 70 goals this year, and the Red Bulls allowed a league-low 33.

Miguel Almirón and Josef Martínez are MLS' most prolific attacking duo, with 43 goals and 20 assists combined this year. Red Bulls centerback Aaron Long won Defender of the Year honors, and Kemar Lawrence joined him on the season's Best XI. Tim Parker was also superb on the back line, and defensive midfielder Sean Davis was a quiet stalwart. With Atlanta likely to again draw a crowd of over 70,000 fans for the first leg, New York has a big job ahead.

2. Will Tata Martino or Tyler Adams say goodbye to MLS first? The Atlanta manager and the Red Bulls star midfield are both expected to leave for other countries when their seasons end. Martino is reportedly ticketed to be the Mexican national team's next head coach, after being ignored by the U.S. Soccer Federation for reasons they've refused to admit. Adams will join Germany's RB Leipzig, owned by the same energy drink behemoth that runs the New York Red Bulls, for a transfer fee likely around $5 million.

Both men's moves are on hold until their respective seasons end. One of them will happen a week sooner than the other.

3. The Red Bulls' history of heartbreak. New York isn't the only MLS original team to never win the biggest prize in the league's 23-year history. Dallas and New England haven't either. But the Red Bulls are the only original team that's never won MLS Cup or the U.S. Open Cup. While the three Supporters' Shields since 2013 are a testament to how good the club has been in recent times, they and their fans still crave the trophies that matter most.

If New York comes home with the score close, the second leg at Red Bull Arena should be an epic occasion. (Perhaps New York-area soccer fans will finally show up on a weeknight?) To raise the stakes even more, the winner of the Eastern final series will host the championship game on Dec. 8. Will this finally be the year the drought ends?

Western Conference: 1. Sporting Kansas City vs. 5. Portland Timbers

First leg: Sunday, 7:30 p.m. at Providence Park, Portland, Ore. (Fox Sports 1 and Fox Deportes, FoxSportsGo.com)
Second leg: Thursday, 9:30 p.m. at Children's Mercy Park, Kansas City, Kan. (ESPN, ESPN Deportes, ESPN.com/Watch)

Three storylines

1. Portland is no ordinary 5-seed. The standings don't lie, but it's hard to call a team with with playmakers Diego Valeri and Sebastián Blanco an underdog. Especially a team that calls Providence Park home. The grand old barn at the heart of Soccer City, USA will be as raucous as ever on Sunday, and the Timbers will need to push for as big a win as they can muster.

History will haunt Sporting when they arrive in Cascadia. These teams have only met once in the playoffs before, but it was a game for the ages. Their first-round matchup in 2015 finished 2-2 in 120 minutes, then went to a penalty shootout that lasted 11 rounds. Kansas City's Saad Abdul-Salaam's ninth-round kick hit both posts but didn't go in. It's been called "The Double Post Game" ever since, and in its honor, the Timbers built a beer concession stand under the stadium's north end called "The Double Post Bar."

2. Who will start up top for the Timbers? Samuel Armenteros, Portland's No. 1 striker, has missed all three playoff games so far due to injuries. Second-year Duke product Jeremy Ebobisse has been solid as his replacement, including a fine goal in the first leg of the conference final against arch-rival Seattle, but Armenteros is the better player.

Armenteros resumed training at the start of the week, which is a good sign. He has the pace to break through opponents' lines, and the creativity to get out of tight spaces. The Timbers need every weapon they can muster against a Kansas City team that's disciplined, presses high and can turn teams over fast.

3. Kansas City's chance to shed its no-name image. Even most MLS aficionados don't pay too much attention to Ilie Sánchez, Johnny Russell, Dániel Sallói and Felipe Gutiérrez. But those four players — from Spain, Scotland, Hungary and Chile, respectively — play some terrific soccer. In the regular season, Sporting led the league in goals from open play (50, tied with the L.A. Galaxy), shots per game (17.1), passing accuracy (83.6%) and aerial duals won (54.6%); and ranked second in possession (56.8%).

If Sporting wins the series and advances to the MLS Cup final, it will be their second trip to the title game in Delran-born manager Peter Vermes' nine-year tenure. The first was five years ago, and the money in MLS has grown exponentially since then. Reaching this year's title game would be an immense feat for the team in MLS' second-smallest media market (No. 33 nationally). And it should be a lesson to the Union about how badly they've gotten things wrong.