Reims - United States captain Megan Rapinoe said hammering Thailand 13-0 in the Women's World Cup was all "part of growing the game" after a win so lop-sided there were suggestions they should have eased up to save the Thais from embarrassment.

Rapinoe scored the ninth goal for the title-holders, one of 10 in the second half as the USA surpassed the tournament record of 11-0, set by Germany against Argentina in 2007.

"We have the utmost respect for everyone we play but it's the World Cup and that's part of it. It's part of growing the game. They'll improve from here," said Rapinoe.

Alex Morgan starred with five goals in the Group F opener in Reims, in Champagne country, as the USA pulverised a Thailand side playing at just their second World Cup.

This was always going to be a daunting challenge for the Chaba Kaew, who made it to France thanks to their run to the semi-finals at last year's Asian Cup.

"There are some teams here that, since the last World Cup, have only played a handful of games, or only the qualifiers. It's embarrassing for the federations, and for FIFA as well," said Rapinoe as she reflected on the gulf between the world's top sides and the rest.

Not that Thailand are necessarily minnows, as they sit 34th in the FIFA rankings, higher than six other sides competing at this World Cup.

'Feet on the ground'

One TV commentator said the win was so comprehensive that the USA should have stopped attacking late in the game, when the result wasn't in doubt.

But the 33-year-old Rapinoe said the champions were happy to snatch the goals record from Germany as they go in search of their fourth world title.

"I was hoping we'd beat Germany! I had that in mind," joked Rapinoe.

"I didn't really think about that while we were playing but right when we walked off. We always want to have any world record and anything we can get over the Germans, we'll take it."

As well as Morgan's five goals, Rose Lavelle and Samantha Mewis both scored twice, while there was one goal each for Lindsey Horan, Rapinoe, Mallory Pugh and veteran Carli Lloyd.

Goal difference may be important in deciding who wins the group, with the USA facing Chile next before taking on Sweden, the team who defeated them in the quarter-finals of the Rio Olympics in 2016.

However, if they win the group, they could end up facing hosts France in the quarter-finals.

"I definitely think we need to keep our feet on the ground and I think we will, but I do think that we created a lot of good energy and that's something that can help carry us forward," said Mewis, the 26-year-old midfielder who was making her World Cup finals debut.