With just 180 minutes separating the eight remaining teams from moving to the Conference Championships or ending their season, each coaching decision is crucial. Here are four of the biggest decisions the tacticians faced in Leg 1:
Berhalter's Higuain decision
Prior to playing 90 minutes on Decision Day, Federico Higuain had gone kick off to final whistle just once since June. Then, he logged 120 minutes on Wednesday against D.C. United. To ask for another 90 minutes would be difficult, so Gregg Berhalter had a decision to make: start Pipa, get as many quality minutes as you can and hope he isn't a step off the pace or leave him out of the starting XI and use him as an impact substitute.
Berhalter elected for the latter and it worked perfectly. He even changed the system to start, sticking Patrick Mullins up top with Gyasi Zardes around him, looking to play long, bypassing RBNY's vaunted press. At halftime, Mullins was withdrawn for Higuain and the 34-year-old made the most of his 45 minutes.
Higuain's sublime assist to Zardes is the difference between the sides heading into leg two at Red Bull Arena.
Oh, the ecstasy and despair that can come in 45 quick minutes on a soccer field.
The Sounders raced out to a quick 1-0 lead on the road against the Timbers but, by halftime, they were down 2-1 and had been forced by injuries to substitute Chad Marshall and Cristian Roldan. Marshall is an MLS Defender of the Year finalist while Roldan had played all but seven minutes this season. Brian Schmetzer was dealt a bad hand.
Schmetzer opted to introduce Waylon Francis for Roldan then Roman Torres for Marshall. Both worked fine, managing the damage and limiting Portland to just the 2-1 lead on aggregate as the sides head to Seattle.
Tata: First or second half Miggy?
Working to recover from a hamstring injury, Miguel Almiron's status for Leg 1 against NYCFC was in question but he was able to return to partial fitness in time to play. Tata Martino had to decide if he wanted Almiron back in the starting XI, surely not to play the full 90, or off the bench against tired legs for a second-half boost.
Tata opted to reinstate Almiron to the lineup to great effect. Almiron had a goal called back for offside and helped Atlanta keep the pressure on NYCFC before being taken off at halftime with a 1-0 lead. While folks at MLSsoccer.com headquarters watched the game, Matt Doyle pointed out that Almiron starting the first half rather than coming off the bench could be down to how important he is to setting the tone for his side's style and intensity.
Vermes' left-back conundrum
With Seth Sinovic suspended for the first leg, Peter Vermes recalled US U-20 fullback Jaylin Lindsey to the squad with a hole at left back. That hole would be filled by attacker Yohan Croizet in the back, who he brought on in that position for 26 minutes on Decision Day, or Lindsey, an 18-year-old Homegrown and natural right back.
Vermes gave Croizet the nod and the Designated Player adapted well to the new position. He was the team's most successful player in duels (89 pct) and made the most tackles (7). Defending for large swaths of the game -- SKC finished with just 33 pct possession, the least they've had in a game since 2015 -- Croizet did as well as could have been expected.