With Chicago's loss tonight to New England tonight, the Fire can no longer catch Sporting, meaning that KC is guaranteed a top 2 finish in the East and will have the second home game (a midweek game) in the conference semifinals.
DC's late win against Columbus though means that Kansas City has not clinched the East yet. The first tie breaker this year is goals scored, not goal difference or head-to-head record. What that means is that if KC loses at home to Philadelphia and DC defeat Chicago on the road next weekend, United will likely win the East. With goals scored being the first tiebreaker, if KC were to lose, they would have to make up the 12 goal difference that DC currently has on KC in goals scored if they were to lose. For example, if KC were to lose 16-15 on Wednesday and DC wins 1-0, KC would technically win the East because they'd have scored 55 goals to DC's 53 in that scenario.
The easy way to resolve all of this is to take care of business on Wednesday, a point in the home finale against Philadelphia and Sporting KC will clinch the East. It's that simple, get a result and none of this matters. A point puts KC on 61 points, out of reach of DC's max of 60.