A goal wiped away after a video review and a red card given to Brad Guzan were enough to end Atlanta United’s eight-game unbeaten streak in a 2-0 loss to Sporting KC on Wednesday at Mercedes-Benz Stadium.

In a game billed as a possible MLS Cup preview between the team with the most points in the East against the best team in the West, Daniel Salloi’s goal in the 67th minute proved the difference in front of 44,696 who battled horrible traffic to get to the match.

» More: What Atlanta United players said after loss

Atlanta United’s Kevin Kratz twice had chances to tie with free kicks late in the game, but Sporting KC goalkeeper Tim Melia made two outstanding saves.

“I think we played well,” Atlanta United’s Leandro Gonzalez Pirez said. “Up until the red card, I think we were deserving of winning the match then the red card changed things. I'm not going to argue that it’s a foul, but for me, I didn't think it was worthy of a red card because the ball was going out of bounds and I ran back to cover the goal.”

By the time Salloi scored, Atlanta United  (7-2-1) had been playing with 10 men for the previous 33 minutes following a red card to Guzan after he took down Khiry Shelton just outside of the penalty box in the first half.

Shelton had run past Michael Parkhurst and onto a well-hit pass from Yohan Croizet. Guzan had no choice but to slice down Shelton with a hard tackle. Referee Mark Geiger immediately pulled out a red card. The card means Guzan will miss Sunday’s game against Orlando. It was the first red card Guzan has received in his MLS career.

Paul Christensen, signed on Tuesday to an emergency loan deal, was put in goal for Atlanta United. Christensen was in because of injuries to backups Alec Kann (knee) and Mitch Hildebrandt (knee). Christensen was the team’s fourth-round selection in this year’s SuperDraft, but had yet to play in MLS. He has played for Atlanta United 2, the team’s USL affiliate. Christensen was also signed to an emergency loan deal before last week’s game at Chicago.

“It’s a tough spot for him, you know, just being called up for a few games (and) not thinking he’s going to play,” Parkhurst said. “To step in, down a man, I thought he did really well. He communicated well. He made that big save for us early in the second half. So, kudos to him for being ready and stepping up in a tough spot.”

Atlanta United has experience playing a man down for long stretches. Centerback Leandro Gonzalez Pirez was given a second yellow card in the 36th minute with his team leading 1-0. Atlanta United held on for the remaining 54 minutes to win. But they had the lead when Pirez was ejected. Wednesday’s game was still tied.

Christensen made his first tough save five minutes into the second half when he stopped a shot with his chest in a one-on-one situation near the top of the penalty box.

Sporting KC broke through in the 67th minute when Salloi curled a shot from 20 yards into the lower right corner past a diving Christensen. Salloi was given a lot of space before his shot.

Atlanta United had a good chance to tie in the 83rd minute when Kratz lined up a free kick from 21 yards away. Having already scored two goals this season on free kicks, Kratz again put the shot on goal, but Melia scrambled across and got enough to keep the ball from going in.

Kratz got another chance near the same spot in the 86th minute but Melia was again equal to the task.

“We spoke about it at half time,” Atlanta United’s Jeff Larentowicz said. “We wanted to be solid defensively but also when we had our opportunities to break we wanted to do that. Luckily, we’ve got three of the better players in the league at counter attacking and creating chance with very little. I thought they did that pretty well. They bring Kevin (Kratz) on and he has two opportunities that are right in his wheelhouse and (Sporting Kansas City goalkeeper Tim) Melia makes some good saves.”

Sporting KC put away the game with a goal by Gerso Fernandez in the 87th minute. Fernandez looked to be yards offside when he received the ball.

Guzan’s red card wasn’t the only eye-opening moment in the game.

Atlanta United manager Gerardo Martino threw in a surprise by switching back to the 4-2-3-1/4-3-3 formation that helped the team reach the playoffs last season. It hasn’t been used a great deal since the season-opening 4-0 loss at Houston. After that, Martino switched to a 3-5-2. As part of the formation switch for Wednesday’s game, Martino was able to start Josef Martinez, Hector Villalba, Miguel Almiron and Ezequiel Barco for the first time.

“We decided to play in this formation because of the style that Kansas City plays,” Martino said. “They are a team that likes to build out the back. We knew that if we played in our 4-2-3-1 system that we had to pressure those guys one-on-one all the way up the field, and if we had stuck with our five at the back system we would have let them play out of the back without any pressure and that would have opened up all of their passing lanes that they like to create. I thought before the game, and I still think, that this formation was the best way to play against teams like Kansas City that like to build out of the back.”

The switch weakens the offense in terms of numbers, but strengthens the defense. As part of the formation switch, Martino gave right fullback Sal Zizzo his first start and benched Julian Gressel, who started the previous nine games. Part of the switch may have had to do with injuries to centerbacks Franco Escobar (chest) and Chris McCann (hamstring), as well as the game at Orlando on Sunday.

It didn’t take long for the system to work.

First, Pirez stopped a Sporting KC attack, and then dribbled up the field for 30 yards before finding a teammate. Barco wound up the ball, and went on a mazy run. His pass bounced off a Sporting KC defender and to Martinez, who slotted it home. But Martinez was yards offside. Geiger went to the replay system and, after confirming that Martinez received the ball in an offside position, ruled no goal.

Atlanta United came close in the 15th minute when Darlington Nagbe chipped a pass close to the 6-yard box to an onrushing Villalba, who hammered a volley that Melia palmed away.

Sporting KC started to create its own chances, with Shelton heading wide from 7 yards away in the 33rd minute.

Atlanta United stormed back down the field with Villalba missing the goal from 6 yards.

“Probably the best team in the league, I’d say,” Sporting KC manager Peter Vermes said. “They are. Probably make the comparison – years ago, you remember ‘The Greatest Show on Turf’ with the Rams? It’s kind of the same thing here too. I told Tata (Martino) this is a great environment, this club has done an unbelievable job, the stadium, the players that they have brought in, the way they built their team, fans obviously are connected with the way they play.”