On a night when Timbers were without head coach Giovanni Savarese, who is traveling to Italy because of an urgent health issue with his father, Portland easily had the better of the chances before the break.
And although LAFC threatened more regularly during the second half, Ebobisse's 84th-minute strike, kept onside because of a touch from defender Jordan Harvey, gave the visitors a deserved win.
It will be a bitter defeat for the hosts and coach Bob Bradley, who clearly fielded his best XI and will now have to deal with how to mange another MLS game in less than 48 hours' time. Portland, meanwhile, triumphed while resting talisman Diego Valeri for most of the match, until he came on late to spell the goal scorer.
- 84' - POR - Jeremy Ebobisse | WATCH
- THE BIG PICTURE: LAFC may yet finish 2019 as one of the all-time great MLS sides, but for now at least, it appears there will be no American domestic treble. Still no U.S. club has accomplished the feat, although Toronto FC won the Canadian version (Canada Championship, Supporters' Shield, MLS Cup) in 2017.
- MOMENT OF THE MATCH: Though both teams created a couple cleaner looks, this always had the feel of the kind of cup tie that would be decided by a random bounce, slip or deflection. That happened when Harvey inadvertently played the ball directly into the path of Ebobisse, who wasn't about to waste his good fortune.
- MAN OF THE MATCH:Jorge Moreira. A consistent threat down the right flank in Portland's attack, while also keeping Diego Rossi relatively in check. It was a difficult assignment Wednesday night, but the fullback on loan from River Plate made it look relatively simple.