SKC will be the happier of the two side, having gone on the road to take on Panama's Independiente de la Chorrera and scored a vital away goal in a 2-1 loss.
Romeesh Ivey opened the scoring for the home side just before halftime, but an Ilie Sanchez strike from the penalty spot had the MLS side back level six minutes after the restart.
But the home side would come out on top thanks to a stunning strike from Alexis Corpas, who found the top corner from 25 yards out near the hour mark to earn a result for the Panamanian outfit.
"This is definitely not the result we wanted, but we still have the second leg in Kansas City," Sanchez told Concacaf's site following the match.
The result does leave some hope for Sporting, who now need either a two-goal victory or a 1-0 result at home to be sure of a place in the semifinals.
"We would have liked to score another one to tie the game at least, but in the end scoring here in a very tough place with these fantastic fans, it's important for us," Sanchez said. "But we lost the game, we are not happy and we hope to come back next [Thursday]."
For Atlanta United, hopes of a comeback look extremely slim following a 3-0 dismantling at the hands of Mexican outfit Monterrey.
A Nicolas Sanchez penalty inside the opening 20 minutes put Rayados out in front, but Atlanta seemed to have calm things down before a late onslaught from the home side put the match to bed.
Dorlan Pabon's doubled Monterrey's lead in the 80th minute before floating in a cross for Jesus Gallardo to slam home four minutes.
The late strikes will come as a hammer blow to Atlanta United, though the MLS side will take some hope from turning around its last-16 tie against Herediano after losing the first leg 3-1 away from home.
Atlanta will host Monterrey next Wednesday, while Sporting Kansas City will face its home leg against Independiente on Thursday.