The USA, who lifted the trophy for the third time in Canada in 2015, were heavy favourites to beat Thailand in their first game in Group F in the city of Reims, in Champagne country.
There were four survivors in their line-up from the team that started the final against Japan four years ago, when Carli Lloyd scored a hat-trick in a 5-2 victory in Vancouver.
Lloyd was left on the bench this time by coach Jill Ellis, but star striker Alex Morgan was among the starters along with Megan Rapinoe, who wore the captain's armband.
The 33-year-old Rapinoe has been a leading voice in the USWNT's much publicised fight for pay equality that saw them file a lawsuit against the United States Soccer Federation in March accusing the organisation of gender discrimination.
It is an intimidating assignment for the Thais, who are only appearing at their second World Cup.
A large American presence in Reims ensured that the match was one of 13 confirmed sell-outs in the competition, FIFA revealed on Tuesday as they said that more than a million tickets had now been sold for the tournament.
The United States have never failed to make the semi-finals at the World Cup, but their incredible record at the Olympics -- four golds and one silver from five appearances -- came to an end when they were beaten by Sweden in the quarter-finals in Rio three years ago.
Sweden are in the same group here in France and they started their campaign with a 2-0 win over Chile in Rennes, but only after a long hold-up because of torrential rain which led to conditions deteriorating.
Rain had been falling for around a quarter of an hour amid a threat of thunderstorms when the Mexican referee, Lucila Venegas, decided to take the players off in the 72nd minute with the score still 0-0.
Play eventually resumed following a break of around 40 minutes, and former Paris Saint-Germain and Manchester City midfielder Kosovare Asllani fired into the roof of the net to give Sweden the lead in the 83rd minute.
Substitute Madelen Janogy ran through and smashed in the second goal in injury time to wrap up the win for the Swedes, the 2003 World Cup runners-up.
"In general we are stronger than our opponents and the final 20 minutes are important for us," said Asllani.
"The interruption definitely upset us. We didn't want it to end 0-0, so we wanted to come back out and decide the game and I think we deserved the three points."
Dutch strike late
Meanwhile, European champions the Netherlands also got off to a winning start, but left it very late to beat New Zealand in Le Havre.
Jill Roord came off the bench and headed home from close range in added time to give the Dutch a 1-0 victory, putting them level with Canada at the top of Group E.
"I'm very relieved, of course," said the Dutch coach, Sarina Wiegman, after her team dominated proceedings but were almost forced to settle for a point.
It was a deeply disappointing result for the Football Ferns, who had resisted so well for long spells at the Stade Oceane.
"The players will be absolutely devastated but we're a resilient group and I'm pretty confident we'll bounce back," said New Zealand coach Tom Sermanni.
Elsewhere, Germany coach Martina Voss-Tecklenburg revealed that star player Dzsenifer Marozsan may miss the rest of the World Cup after being ruled out of Wednesday's crucial Group B clash with Spain due to a broken toe.
"Anyone who has broken a toe knows how much it hurts," said Voss-Tecklenburg, who described the 27 year-old as "irreplaceable".