Dirk Nowitzki led the Mavericks with 28 points, 11 rebounds and three blocked shots.
Jerry Stackhouse added 29 points for Dallas, which has won seven of its last nine games. Jason Terry had 26 and Michael Finley contributed 25, as the Mavericks posted the highest point total in the NBA this season.
Gilbert Arenas scored a career-high 43 points for Washington, which has lost two straight on the heels of a seven-game winning streak. Both losses have come with Larry Hughes on the injured list with a fractured thumb.
The Mavericks played their last game before Coach Don Nelson undergoes shoulder surgery Thursday. Nelson is expected to be out until mid-February and assistant Avery Johnson will run the team in his absence.