Real Salt Lake continued their giant-slaying run with another upset, this time stunning Sporting Kansas City 2-1 at the death to reach the Western Conference final in the MLS Cup play-offs.

After eliminating Seattle Sounders on penalties in the opening round, RSL were at it again on Sunday as they produced a second-half comeback to end Sporting KC's season in dramatic fashion.

Sporting KC appeared on track thanks to Johnny Russell's 24th-minute penalty before the seventh-seeded RSL – who were making their 10th Conference semi-final appearance, only Seattle have managed more (12) since 2008 – made their move.

After almost falling 2-0 behind when Gadi Kinda's free-kick was headed off the post, RSL substitute Anderson Julio equalised 18 minutes from the end.

Bobby Wood completed the comeback in the first minute of stoppage time, finishing past Sporting KC goalkeeper Tim Melia.

RSL will next face Portland Timbers for a spot in the MLS Cup decider.

Elsewhere, Nashville missed all four of their penalties as Philadelphia Union prevailed 2-0 in the shoot-out to book a spot in the Eastern Conference final for the first time in the club's history.

Penalties were needed after Hany Mukhtar's opener was cancelled out by Union star Daniel Gazdag in Philadelphia.

But it was a painful shoot-out for Nashville, who were unable to find the back of the net as Andre Blake made two saves to help the Union through.

Next up for the Union is a date against either New England Revolution or New York City.