Petermann, one of three German players who attend U.S. colleges, broke the scoreless deadlock in the end-to-end match in the 65th minute. After a turnover by Andi Sullivan in the German half, Petermann broke free and her pace was too much for the American defenders. Panfil finished with equal coolness in the 90th minute to put the game away.
Both the USA and Germany had plenty of chances, though the best ones fell to the Germans, the 2013 European runners-up behind France.
U.S. defender Katie Naughton cleared one German shot off the line with goalie Katelyn Rowland out of position, and Lina Magull couldn't believe her bad luck as she had a shot deflect off Naughton's foot and off the post.
Paris St. Germain star Lindsey Horan was the best U.S. player, but she had no answer for German goalkeeper Meike Kaemper, who finished with 16 saves. Rowland had 10 saves for the USA.
American Cari Roccaro and Magull were the only players who also played in the 2012 final in Japan. Kaemper was a back-up keeper two years ago. German senior national team star Melanie Leupolz, another eligible player from the 2012 team, was scratched from the U-20 World Cup because of an injury.
In other play on opening day, Ghana stunned host Canada, 1-0.Aug. 5 in Edmonton, Alb.
USA 0 Germany 2. Goals: Petermann 65, Panfil 90.
USA -- Rowland; Amack, Roccaro, Naughton, Basinger; Lavelle, Sullivan (Baldwin, 74), Pugh; Purce (Green, 77), Horan, Jordan (Doniak, 46).
Germany -- Kaemper; Wilde, Rauch, Gidion, Knaak, Magull (Dallmann, 60), Panfil, Daebritz (Schermuly, 79), Dieckmann; Bremer, Petermann (Meister, 72).