Atlanta United’s Julian Gressel said there is no need to make this complicated.

Win or draw to defend his team's 1-0 lead against NYCFC when they meet in the second leg of the Eastern Conference playoff semifinal on Sunday at Mercedes-Benz Stadium.

If Atlanta United can draw or defeat NYCFC, it will advance to the Eastern Conference finals, where it will face either New York Red Bulls or Columbus. If Atlanta United allows more than two goals and loses by at least one goal, it’s season is done. There are scenarios for extra time or penalty kicks but Atlanta United would rather not go there, especially after last year’s knockout round loss to Columbus on penalty kicks.

NYCFC has already said it is going to approach this game as if it’s a final. It should. If it doesn’t defeat Atlanta United, which is 11-2-4 at home this season, its season is over.

“It’s 90 minutes, 90 minutes at home against a good team that can score goals, so we are going to have to be prepared defensively, obviously very clued in like we were in New York,” Gressel said Tuesday.

Atlanta United held NYCFC without a shot on goal in last week’s win at Yankee Stadium. That was a first this season for the Cityzens in the way-too-comfy confines in the Bronx.

Playing a tenacious defense that used three centerbacks and five midfielders, two of which sometimes dropped into the backline to make five centerbacks, Atlanta United played with as much effort as in any game this season. Though it committed 21 fouls, just two players, Eric Remedi and Hector Villalba,  received yellow cards for rough play.

“Keep them with zero shots on goal, that’s what you need, that’s what we did on Sunday and hopefully we can do that again this Sunday,” fullback Greg Garza said.

The defensive plan will likely be as simple this week as it was last week: avoid mistakes and keep things simple.

That was stressed by manager Gerardo Martino during last week’s training sessions. Gressel said during one session the team was making mistakes as it tried to pass the ball from its penalty box forward. Martino called the group together and told them they needed to be better. Take the simpler decision. In Yankee Stadium, that meant either booting the ball back downfield, or simply kicking it out of bounds.

"The message to the team was not to make costly mistakes because I know that if we can do that, I like our chances of winning,” Martino said after Sunday’s win.

Though Atlanta United completed far fewer passes, because the ball didn’t spend a lot of time under control in Atlanta United’s half the tactic minimized the ability of striker David Villa’s and NYCFC’s talented midfielders from influencing the game.

“Clear message throughout the week,” Gressel said.

Trying to use the same defensive shell may be more difficult on the larger pitch of Mercedes-Benz Stadium. There will be more space to try to defend. Atlanta United allowed 19 goals at home this season, tied for fifth-most among the 12 playoff teams. NYCFC scored two in its game at Mercedes-Benz.

“We know we can score goals there so yeah, I’m not worried,” NYCFC midfielder Alexander Ring said. “I’m looking forward to it. Like I said, playoffs are what we’ve been working for all year and I’m sure we are going to bring our ‘A’ game when we show up there.”

However, if NYCFC pushes players forward to try to get that tying goal, it will open up space in its half of the field that Atlanta United can exploit. The Five Stripes, one of the best counterattacking teams in MLS, had at least two opportunities to take a 2-0 lead at Yankee Stadium, but didn’t capitalize when those breakaways fizzled out.

“I think you can try and take away the dimension part of it with that field being so small,” Garza said. “As long as we continue to try to find that attacking break that we have with getting guys forward and being lethal up top, and take from that game the defensive unit we had throughout the whole entire game.

“Take those two things we’ve done all season, and in particular that game, and take them to the next game and hopefully come out on top.”