The game, which saw Portugal's Silvestre Varela snatch a last-minute equaliser to break American hearts, was watched by an average of 18.2 million viewers on ESPN, according to early ratings data. A peak of 23 million watched during the final half-hour.
The previous record TV audience for a soccer match in the US was 18 million for the Women's World Cup final in 1999, in which the US beat China in a penalty shootout.
The viewing figure also represents a significant increase on the USA's first game of the tournament in Brazil, a 2-1 victory over Ghana, which was seen by 11.1 million.
The USA currently sit three points clear in second in Group G, but could still be eliminated if they lose their final game against Germany and Portugal beat Ghana by decent margins.