For the second consecutive season, the Union finished runners-up in the 2015 U.S. Open Cup, this time to Sporting Kansas City.

Sakiewicz was replaced with former U.S. men's national team player, Earnie Stewart, who was named Sporting Director in October 2015.

In that round, the Union defeated the Harrisburg City Islanders, a team in the third tier of the American soccer pyramid, 3-1 after extra time.

The Union then defeated the New England Revolution 2-0 in the quarterfinals and FC Dallas 4-3 on penalty kicks after a 1–1 tie in the semifinals.

[3] Note: Flags indicate national team as defined under FIFA eligibility rules; some limited exceptions apply.