The reigning champions were given an almighty scare in their 0-0 draw with Portugal on Tuesday night, a match they largely controlled but almost let slip.
Portugal substitute Ana Capeta smashed a 91st-minute effort onto the post when a goal would have eliminated the two-time reigning champions.
Instead, the world No.1s limped into the round of 16 at the expense of the first-timers, who were brave and on another night might have upended world football's order.
Capeta's moment was so huge that half of the Portuguese bench jumped up ready to celebrate a famous victory.
"I swear, I truly believed the goal would be in that moment," coach Francisco Neto said.
"Unfortunately we don't win and we go home. But our girls were very brave and they made an amazing game today."
Portugal had another stoppage time chance when Alyssa Naeher flapped at a floating ball from a deep free kick, which drifted just wide.
The Portuguese collapsed on the ground in despair at full time while the Americans looked sheepish after their performance.
"It's not the result we wanted," striker Alex Morgan said.
"We missed some big chances. I did as well. We own that.
"Now it's coming back together, knowing we have all the pieces to make it all the way."
The result means the US qualified in second place in Group E, trailing the Netherlands who thumped Vietnam 7-0 in Dunedin on Tuesday.
A return of five points is the Americans' worst group-stage performance at a Women's World Cup, failing to top their group for just the second time.
It just didn't quite click in Auckland for the USWNT who are yet to impress in New Zealand.
The result means the US will face the winners of Group G - most likely Sweden - on Sunday in the round of 16.
Should the Scandinavians avoid defeat against Argentina as expected, the world No.1s will meet the world No.3s in a blockbuster Melbourne meeting.
On Tuesday night in Auckland, Neto shook up his team with six changes and saw his side battle superbly in midfield.
They might have pinched a goal early when Francisca Nazareth split the US defence to put Jessica Silva through on goal, only for the winger to scuff her shot.
There were two changes for the US with Lynn Williams in for Trinity Rodman and superstar Rose Lavelle starting her first game for three months after a knee injury.
Both were prominent in the first half when Williams prodded a loose ball over the bar from Alex Morgan's superb touchline dribble.
Williams had a fine chance to break the deadlock in first-half injury time only to lash a volley straight at Ines Pereira.
Diana Gomes produced a goal-line clearance on 54 minutes when Morgan rounded the goalkeeper and attempted to tap home from a wide angle.
Megan Rapinoe joined the fray on the hour mark but the chances failed to come against the well-organised Portugal team.
The game opened up late with both sides in search of a winner with the Portuguese coming closest.
Silva cried as she lamented the lost opportunity.
"We are really very sad about the result," she said.
"Don't forget about us. Please realise what Portugal has achieved."
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