A primetime time slot helped yield 5.261 million viewers, it said.
The Americans got their bid for an unprecedented three-peat off to a comfortable start as they beat World Cup newcomers Vietnam3-0 in Auckland on Saturday, with the match peaking at 6.552 million watchers for the English-language broadcast.
That was a 99% increase from the 2.649 million who tuned in for their 13-0 rout to open their 2019 campaign, when the match was aired mid-day on the U.S. East Coast.
The numbers were up 59% from their 2015 equivalent match, Fox said, when the Americans kicked off against Australia in Canada around 7 p.m. on the East Coast. That match was aired on Fox's FS1 channel.
While this year's primetime time slot offered a clear advantage over 2019, the match competed domestically for attention with Lionel Messi's highly anticipated Major League Soccer debut.
Messi, perhaps the biggest star to sign with the top-flight North American league since David Beckham 16 years ago, scored a stoppage-time victory in front of a star-studded crowd for the match, which kicked off about an hour before the U.S. team.