The former England captain bent a glorious effort over the wall and into the top corner in the 18th minute, his 10th goal of the Major League Soccer season.
Victory strengthened United's hold on a play-off spot in the Eastern Conference.
Sporting Kansas City scored four times inside the final half-hour to come from 1-0 down to win 4-1 at the Vancouver Whitecaps, whose play-off hopes now hang by a thread.
Trailing to Felipe's 43rd-minute goal, the visitors levelled through Yohan Croizet before Daniel Salloi put them ahead eight minutes from time.
At the death Gianluca Busio added a third and Salloi made it four.
The Seattle Sounders also won away, triumphing 2-1 at Orlando City to seal their place in the play-offs.
Goals from Victor Rodriguez and Handwalla Bwana had them two up after only 13 minutes, with Dominic Dwyer pulling one back in the second half for the hosts.