ATLANTA -- Daniel Salloi and Gerso Fernandes scored second-half goals and Tim Melia came up with several huge saves, leading Sporting Kansas City to a 2-0 victory over short-handed Atlanta.
The loss snapped United's eight-game unbeaten streak Wednesday night in a showdown between the two conference leaders in Major League Soccer.
United played the last 56 minutes a man down after goalkeeper Brad Guzan was given a red card for taking out Kansas City's Khiry Shelton just outside the penalty area as he broke in all alone on goal.
Rookie Paul Christensen, an emergency signee filling in for injured backup Alec Kann, made a big save shortly after entering but couldn't hold off a Sporting team with an extra player.
In the 67th minute, Salloi curled a shot from beyond the box to beat a diving Christensen just inside the right post. In the closing minutes, with United pressing forward in search of the tying goal, Fernandes took a long pass and went in all alone on Christensen, deking the 22-year-old keeper and guiding the clinching goal into an open net.
Melia made eight saves, including a pair of acrobatic stops on free-kick specialist Kevin Kratz that could've allowed United to escape with a point. Finishing off the clean sheet, Melia got a hand on Miguel Almiron's last-gasp attempt, knocking the ball off the post and leaping on top of the loose ball.
Almiron walked away shaking his head, and the referee blew the whistle to end the game. Melia was swarmed by his teammates, celebrating his brilliant performance before a crowd of 44,696 at Mercedes-Benz Stadium
Until Guzan's flagrant foul, United had largely controlled play in the opening half.
Josef Martinez appeared to put the home side ahead in the sixth minute after collecting a deflected pass in front of the goal, losing defender Ike Opara with a nifty move to his left foot and ripping a shot past Melia. But Martinez was clearly offside, leading to a video review that overturned the goal.
United had several more chances to break up the clean sheet. Melia swatted away a header by Leandro Gonzalez Pirez, got in front of a backfooted flick by Martinez and stuffed a chance by Hector Villalba when he broke free in front of the net from a perfectly timed pass from Darlington Nagbe .
The three points gives Peter Vermes' team an early-season lead in the Supporters' Shield race.