Ertz, a twice Female Player of the Year who played a key role in the team's World Cup winning campaigns in 2015 and 2019, was given an emotional send off with fans holding up messages of appreciation throughout the contest.
"Closure," Ertz said when asked what it meant to see so many fans staying after the game to continue to cheer her on.
"You always want to make an impact in this sport and for this team especially, that's both on and off the field."
Some were hoping that Ertz, who took an 18-month break prior to this year's Women's World Cup to give birth to her son Madden, might be convinced to stay on through next year's Paris Olympics but she said her priorities had changed.
"I've got a little boy that I'm excited to spend my time with," said Ertz, who is married to NFL tight end Zach Ertz.
"Sacrificing time is hard and his face is so cute... but mama can still play!"
Striker Alex Morgan called Ertz "one of the most important players" on the team over the last decade.
"She's going out on her terms and I'm just really happy for her," Morgan said.
Ertz retires with 123 caps for the national team and a National Women's Soccer League (NWSL) career that spanned seven seasons with the Chicago Red Stars before she joined Angel City FC in Los Angeles earlier this year.
Her exit comes at a time of change for the US team, who on Thursday were playing their first match since the team's disappointing round of 16 exit at the Women's World Cup in New Zealand and Australia.
The team, who is currently searching for a new head coach, will bid farewell to Megan Rapinoe when she drops the curtain on her legendary national team career in another friendly against South Africa on Sunday in Chicago.