Reims, France (CNN) Sport is more often than not a brutal place for the underdog. There should always be hope, of course, but it is usually the Goliaths who win. Just ask Thailand, whose players will be chasing red-shirted American behemoths in their nightmares for a number of nights to come.

The 13-0 scoreline was a true reflection of the match. It was a thumping, and it was a night that records tumbled as Thailand suffered the heaviest defeat in World Cup history.

As both teams walked out onto the field for their opening match of the Women's World Cup, the difference in the physical statures of the opposing players was startlingly apparent. Not long after the final notes of the national anthems had faded into the ether so the disparity in quality became obvious, too.

Ominous warning

It took just 12 minutes for the defending champions to open the scoring, Alex Morgan heading home from four yards. That only Rose Lavelle, who would end the night with two goals, and Lindsey Horan had added to the scoreline by halftime was the real surprise.

After the break, the goals quickly came -- four in the space of six minutes, raising the decibels inside Stade Auguste-Delaune, a stadium in France's champagne region which had become a pocket of America for the evening.

Alex Morgan ended the evening with five -- Michelle Akers is the only other player to score as many in a World Cup match -- while Samantha Mewis scored a brace and captain Megan Rapinoe, Mallory Pugh and Carli Lloyd also contributed to the astonishing score.

At the final whistle Thailand's players were in tears. Emotional, beaten, exhausted.

The odds had always been against them. The bookies' thought so, the fans thought so and so did the experts.

This was the world's most successful country in Women's World Cup history, winners of three previous editions of this tournament and favorites in France for a fourth, going up against a nation which was competing in just its second World Cup.

It was No.1 in the world versus No. 34 and these sorts of contests usually end one way, though not quite so savagely. In truth, the gulf between the teams was bigger than the world ranking would suggest.

U.S. stormed to the biggest margin of victory in World Cup history.

Troubled preparation

It had not been a perfect build-up for the Americans. Three months before the start of the defense of its title, 28 members of the current squad filed a class-action lawsuit against the US Soccer Federation, alleging that the federation imposes gender discrimination by paying the women less than the members of the men's national team.

Former goalkeeper Hope Solo has been vocal this week too, telling the BBC that coach Jill Ellis struggled under pressure in 2016, when the team lost to Sweden in the Olympic quarterfinals -- its earliest exit in a major competition.

But the defending champions are eager to make up for the failure of 2016 and the performance in Reims sent out an ominous warning to the teams with hopes of taking the title.

With the US 3-0 up by halftime, the match was effectively over before the second half had begun but Ellis proceeded to make attacking substitutions, bringing on forwards Pugh, Lloyd and Christen Press, decisions she defended after the match in the face of criticisms that the team was too ruthless, too eager to celebrate every goal.

"If this is 10-0 in a men's World Cup are we getting the same questions?" she told reporters.

"A World Cup is about competing. It is about peaking. It is about priming your players ready for the next game.

"You can tell by my substitutions, you play players who can get hot. And if you can play as many hot as you possibly can, feeling good, feeling the back of the net, that's so important for a forward and for a midfielder.

"Those feelings are what can help you through the tournament. We have to come out and we have to play as hard as we possibly can in every game. This will be an incredibly hard World Cup. This is only game one."