Washington was coming off a surprising road win over Miami and was seeking consecutive victories for the first time this year, but the Wizards ran out of steam after almost coming all the way back from a 17-point deficit.
Atlanta captured its second straight and has won nine of its last 11.
The Hawks had a 76-59 advantage with 3:30 to go in the third period, but Washington closed within 85-82 on Kevin Seraphin's jump shot with 8:54 to play in the contest.
Horford then made a pair of layups over the next minute to extend Atlanta's lead to seven points and Washington could get no closer than four the rest of the way.
Josh Smith scored 23 points and grabbed 15 rebounds to pace the Hawks, who shot 48 percent from the floor and outrebounded Washington by 15. Jeff Teague added 19 points and Horford had 14.
Seraphin delivered 19 points and seven rebounds for the Wizards.