Petkovic and her teammates were angered Saturday when an American soloist sang an old version of the German anthem that begins with a stanza considered overtly nationalist -- "Deutschland, Deutschland ueber alles" -- a reference to German supremacy.
Singing that version is unwelcome in Germany because of its strong links to the Nazi era, with only the third stanza of the old anthem now used.
"I have never felt so disrespected in my life," Petkovic said Saturday. "It was an absolute effrontery and insolence of the very worst kind.
Things would get no better for Germany on the court in Maui, Hawaii.
Petkovic, a 12-time Fed Cup singles winner, lost to Alison Riske 7-6 (12/10), 6-2 in Saturday's only completed match.
The US women took a 2-0 lead in the best-of-five tie when Julia Georges, who was in tears after the anthem error, retired Sunday with a knee injury in a rain-disrupted match with Vandeweghe leading 6-3, 3-1.
Georges was hurt slipping on a rain-slicked baseline on the last point played Saturday.
Petkovic was up again on Sunday with the tie on the line, taking on shock Australian Open semi-finalist Vandeweghe.
Petkovic broke Vandeweghe in three of her first four service games to take the first set 6-3, and was up 4-2 in the second when the American took a medical timeout for heat illness.
From there it was all Vandeweghe -- she won the next 10 games to win the match 3-6, 6-4, 6-0 and put the United States into a semi-final tie in April with defending champions the Czech Republic, who beat Spain 3-2.
Petkovic, irked by an extended break allotted to Vandeweghe at the end of the second set, couldn't regain her focus.
She finished with 11 double faults, including two in the final game of the match.
She was then left to stand and watch as Vandeweghe celebrated with her teammates before belatedly shaking hands with her foe.
Even a meaningless doubles rubber played after the tie was decided was a disaster for Germany, as Laura Siegemund and Carina Witthoeft retired while trailing Bethanie Mattek-Sands and Shelby Rogers 4-1 because of Siegemund's left arm injury.
"Honestly, it's been a really tough week for us," said Petkovic, who took to Twitter on Sunday to elaborate on her feelings about the anthem mix-up.
"We were mainly (stunned) and did not know how we react. We feared the whole thing could fall back on us," Petkovic said.
"It is not the worst thing which happened to me in life. But it is the worst thing which happened to me in my Fed Cup life ever."
- Special moment ruined -
Germany captain Barbara Rittner said she had even pondered snatching the microphone from the singer.
"I could have cried, because it is always a special moment, which gives you goosebumps, when you hear the anthem being played," Rittner said.
The president of the US Tennis Association, Katrina Adams, immediately apologized to Rittner in person and promised to investigate.
"The USTA extends a sincere apology to the German Fed Cup team & fans 4 the outdated National Anthem," the US Tennis Association tweeted. "This mistake will not occur again."