Jefferson Savarino scored once in each half for the Claret-and-Cobalt, while Albert Rusnak and Damir Kreilach added insurance goals in the 81st minute to extend RSL’s home mark to 7-2-0.
Savarino deposited the first of his two tallies in the 23rd minute, when he carved through an exposed Union back line to latch on to a long pass from Aaron Herrera.
Fabinho, who started in place of the injured Kai Wagner, failed to communicate properly with Auston Trusty to track the run of Savarino, who easily beat Trusty 1-v-1 for his fourth goal of the 2019 campaign.
The Union were able to tread water for parts of the game, even with Jamiro Monteiro and Ilsinho out injured, but they could not produce anything in the final third to test the RSL back line.
The second mistake that led to a Savarino goal came in the 71st minute, when Fafa Picault and Haris Medunjanin bumped into each other on the Union’s attempt to build out of the back.
Savarino picked up a pass from Kyle Beckerman and finished from the top of the box past Andre Blake, who had four saves on the disastrous night for the Union.
Rusnak’s 81st-minute goal occurred after an individual error in the box by Ray Gaddis, who was waiting for Blake to come up and cover the ball, but that never happened.
Video Review correctly allowed the fourth RSL goal to count in the 89th minute. Kreilach was initially ruled offside, but the review proved he remained onside while receiving a pass from Everton Luiz.
Video Review played a role in overturning a Union goal that would have cut the lead to 2-1. Andrew Wooten struck a perfect shot with his first touch as a Union player, but the ball was ruled out on the left wing before it was crossed into the new signing.
The Union return home on Saturday to take on the Chicago Fire, while RSL hosts Minnesota United in a week’s time.