Christina Aguilera fluffed a line of the Star-Spangled Banner as she belted out a version of the US national anthem to open Sunday's Super Bowl in Texas.
The singer should have sung: "O'er the ramparts we watched, were so gallantly streaming?" but repeated an earlier line with a slight variation.
Aguilera, 30, said in a statement she had got lost in the moment.
The anthem is one of the set piece events of the glittering Super Bowl pre-game ceremony.
Aguilera's mistake immediately set social networks abuzz with chatter.
In a statement released after the performance, the singer said: "I can only hope that everyone could feel my love for this country and that the true spirit of its anthem still came through."
Instead of the correct line, Aguilera actually sang: "What so proudly we watched at the twilight's last gleaming."
The NFL final - which was this year contested by the Green Bay Packers and the Pittsburgh Steelers - is one of the most-watched programmes in US television.
Last year it drew a record 106.5 million viewers.
The half-time show of Super Bowl in 2004 created controversy when Justin Timberlake ripped a piece of Janet Jackson's top, resulting in a glimpse of her right breast.
The pair said the incident was accidental, calling it a "wardrobe malfunction", but broadcaster CBS TV was fined $550,000 (£351,000) after hundreds of complaints from viewers.
The fine was subsequently revoked in July 2008.