Mason hit four 3-pointers whole scoring 19 points and John Wall had a double-double in carrying the Wizards to their first road win in seven tries. Washington's road record improved to 4-16.
Wall had 26 points and 12 assists, hitting 11-of-16 shots from the field.
It was Washington's 10th win of the season, leaving Charlotte (with six) as the only NBA team yet to reach that mark.
The rare Washington win came on the day the Wizards sent JaVale McGee and Ronny Turiaf to Denver in exchange for Nene. They also traded guard Nick Young to the Los Angeles Clippers for forward Brian Cook.
New Orleans was led by Chris Kaman with 20 points and Gustavo Ayon had 16.
The Hornets owned an 81-80 advantage when Washington went on its key run, one that gave the Wizards a 93-81 lead with 3:35 to play.