| Tournament details | |
|---|---|
| Country | United States Canada |
| Teams | 12 |
| Final positions | |
| Champions | Portland Timbers (1st title) |
| Runners-up | Columbus Crew SC |
| Semifinalists | |
| Tournament statistics | |
| Matches played | 17 |
| Goals scored | 46 (2.71 per match) |
| Attendance | 388,289 (22,841 per match) |
| Top goal scorer(s) |  Kei Kamara(4 goals) |
The 2015 MLS Cup playoffs (officially the Audi 2015 MLS Cup Playoffs for sponsorship reasons) was the 20th post-season tournament culminating the Major League Soccer regular season. The tournament began on October 28 with D.C. United defeating New England Revolution and culminated on December 6, 2015, with MLS Cup 2015, the twentieth league championship match for MLS.
Twelve teams (top six per conference) competed, up from ten the last three seasons. The first round of each conference had the third-seeded team hosting the sixth seed, while the fourth-seed hosts the fifth, in a single match to determine who advances to the conference semifinals. In the conference semifinals, the top seed played the lowest remaining seed, while the second seed plays the next-lowest. The winners advanced to the conference finals.
Both the conference semifinals and conference finals were played as two-legged aggregate series, with the higher-ranked team hosting the second leg. If teams were level at the end of the second leg, the away goals rule was used in attempt to determine a winner. If the away goals rule did not resolve the deadlock, 30 minutes of extra time would be played, but the away goals rule will not be applied after extra time. If scores were still level following extra time, a penalty shoot-out was conducted. The winners advanced to the MLS Cup final, a single match hosted by the participant with the better regular season record.
The winner of MLS Cup 2015, the Portland Timbers, qualified for the 2016–17 CONCACAF Champions League. If a Canadian team were to have won the MLS Cup, the next-best team from the United States would have taken their place.
On March 6, 2015, Audi was announced as the official sponsor of the playoffs starting in 2015.
The Portland Timbers won the MLS Cup by defeating Columbus Crew SC 2–1 at the Mapfre Stadium in Columbus, Ohio. The Timbers' Diego Valeri scored the fastest goal in MLS Cup history at 27 seconds, after Crew goalkeeper Steve Clark made a fundamental error by miscontrolling his defender's back-pass, allowing Valeri to strike at the opportunity.
