Yankees general manager Brian Cashman said that the deal made sense because Bruney was eligible for salary arbitration after earning $1.25 million this past season and New York has a certain amount of depth in relief on its 40-man roster.
"He did a fine job for us," Cashman said. "Obviously, we talked to a number of clubs about various players that we had, and Washington expressed an interest in Brian Bruney. We did the deal."
Bruney, 27, opened 2009 as one of Mariano Rivera's setup men, but he went on the disabled list twice with a muscle strain in his right elbow, which he aggravated in May by coming back too quickly from the first DL stint.
In 44 regular-season appearances, Bruney was 5-0 with a 3.92 ERA, limiting opponents to a .243 batting average. In 39 innings, he allowed 36 hits and 17 runs while striking out 36 and walking 23, and he could move into a closing role with the Nats.
"I'm happy with the trade," Nationals manager Jim Riggleman said. "I've seen him pitch a couple of times. He is a power arm who could [be at the end of our bullpen]. We feel we need a little help out there. He has the experience and has a good arm."
Bruney was not on the Yankees' roster for the first two rounds of the postseason against the Twins and Angels, respectively, but he was summoned back for New York's six-game World Series triumph over the Philadelphia Phillies, recording one out and allowing two runs on three hits in a Game 1 loss at Yankee Stadium.
Once a closer with the Arizona Diamondbacks, Bruney signed with the Yankees in July 2006 and immediately impressed, posting a 0.87 ERA in 19 appearances that season. But he battled wildness in '07, posting a 4.87 ERA before being left off New York's postseason roster for the American League Division Series, sent home by former manager Joe Torre.
Though Bruney focused the past two seasons on losing weight and improving his conditioning, both campaigns were interrupted by injuries, including a slip while he was fielding a ground ball at Chicago's U.S. Cellular Field in 2008, resulting in a Lisfranc fracture in the right foot.
Bruney was also involved in a brief spat of words with Mets closer Francisco Rodriguez during the Subway Series this past season.
Earlier Monday, Bruney responded to a rumor that had him possibly going to a different National League East club, the Braves.
"I have no idea," Bruney wrote in a text message. "Obviously, I'm surprised."