The reliever was awarded $1.5 million Wednesday instead of his request for $1.85 million. Arbitrators Steven Wolf, Sylvia Skratek and Dan Brent made the decision a day after hearing arguments.
Bruney, who turned 28 Wednesday, was 5-0 with a 3.92 ERA in 44 regular-season appearances for the New York Yankees last season. He made $1.25 million.
The Nationals acquired the right-hander from New York on Dec. 7 for a player to be named. That ended up being outfielder Jamie Hoffmann, whom the Nationals selected with the first pick of the winter meeting draft.
Bruney pitched just once for the Yankees from mid-April until mid-June last year because of a strained right elbow, an injury he blamed on time he spent warming up during an umpires' video review.
He was dropped from the Yankees' roster for the playoff series against Minnesota and the Los Angeles Angels, then gave up two runs and got just one out in his lone World Series appearance, in the opener against Philadelphia.
Players and owners have split four cases decided thus far, with Milwaukee outfielder Corey Hart ($4.8 million) and Florida outfielder Cody Ross ($4.45 million) winning, and Tampa Bay outfielder B.J. Upton ($3 million) also losing.
Five more players are scheduled for hearings this week: Los Angeles Angels shortstop Erick Aybar and catcher Jeff Mathis; Washington left-hander Sean Burnett; Houston left-hander Wandy Rodriguez and Chicago Cubs shortstop Ryan Theriot.