Visiting Monterrey, which beat Atlanta 3-0 in Mexico last week, won the total-goals series 3-1.
Next up for Monterrey is a semifinal series against either Panama's Club Atletico Independiente or Sporting Kansas City, on April 3 and April 10. CAI won the first leg 2-1 at home last week, with the second leg scheduled for Thursday in Kansas City, Kansas.
Darlington Nagbe set up the goal Wednesday in Atlanta. Dribbling near the top of the 18-yard box, he turned and sent a pass to Martinez making a run behind him. Martinez neatly slotted a 10-yard shot into the top right corner to give Atlanta a victory on the night, but it wasn't enough in the series overall.
It's been a rocky start to the season for Atlanta, the defending MLS champions. Frank de Boer replaced Tata Martino as coach, and his team had one win and one draw through its first five MLS and Champions League games before the victory over Monterrey on Wednesday. And De Boer had to apologize for calling the team's supporters "spoiled."
Atlanta hosts the Philadelphia Union at Mercedes-Benz Stadium at 7 p.m. ET on March 17 (streaming live on ESPN+).