If the Los Angeles Galaxy face the Colorado Rapids in the Western Conference semifinal, Sunday's Union game will start at 4. If the Galaxy play the New York Red Bulls or Columbus Crew, game time for the Union will be 5 p.m.
The other wild-card team is FC Dallas, but the Galaxy can't face Dallas. As the Supporters' Shield winner for the best regular-season record, the Galaxy play the lowest-seeded wild card, and Dallas is the highest-seeded wild card.
The playoffs start Wednesday with the wild-card round when New York visits Dallas. The second wild-card game is Thursday, with Columbus playing at Colorado.
The top three teams in each conference received byes. The Union (8-11-15, 48 points) finished third in the Eastern Conference behind second-place Houston (12-9-13, 49 points) and first-place Sporting Kansas City (13-9-12, 51 points).
The Union's first game of the season, in the third week of March, was against the Dynamo in Houston. The Union used a goal in the fifth minute by Danny Califf to win the opener, 1-0. It was also the debut for goalkeeper Faryd Mondragon, who played a major role in helping the Union earn a playoff berth in their second MLS season.
"The playoffs are a totally different story," Mondragon said Monday after the team's practice at PPL Park. "It has nothing to do with the regular season, and everyone knows these two games have a completely different concept, and we will take it how it is like a final."
In addition to winning at Houston, the Union played the Dynamo to a 1-1 draw on Aug. 6 at PPL Park.
The Union aren't entering the playoffs with great momentum. They clinched a berth with a 1-1 draw on Oct. 15 against Toronto (6-13-15) at PPL Park, then lost their regular-season finale, 1-0, to New York on Thursday at Red Bull Arena in Harrison, N.J. The Red Bulls gained the 10th and final playoff berth with the win.
The Union hope to be energized by the game at PPL Park, where they were 7-1-9 this season.
"It is a well-deserved playoff home game," Mondragon said. "We're looking forward to Sunday, because it will be packed, and PPL Park will explode with joy, and it will be a fantastic afternoon for everyone."
Watch Union goalkeeper Faryd Mondragon talking about the MLS playoffs. Go to www.philly.com/tgk
Contact staff writer Marc Narducci at 856-779-3225, firstname.lastname@example.org, or @sjnard on Twitter.