Was it more evidence that the rest of women's football has caught up?

Or another indication that a once-dominant team is in terminal decline?

Or maybe both?

Whatever the reason, the United States' 2-0 defeat to Mexico at the CONCACAF Women's Gold Cup has left the Americans with everything to prove as the quarter-finals kick off this weekend.

The four-time world champions face Colombia in Los Angeles on Sunday in a game that would once have been seen as a formality for the host nation.

In 12 previous meetings against the South Americans, the US women have never lost, winning 10 times and drawing twice with a for and against goals aggregate of 38-2.

The most recent of those victories was a 3-0 friendly win last October, indicating that the US should be favorites for Sunday's clash at BMO Stadium.

But the jarring nature of Monday's defeat to Mexico -- only their second against 'El Tri' in 43 games -- has re-emphasized that the Americans can no longer take any opponent for granted.

"It shows how far the game is coming," was the verdict of US interim coach Twila Kilgore after watching her team struggle against a vibrant Mexico side.

"There's no easy games any more. And if we don't take care of business and we don't execute, this is to be expected."

The defeat came six months after the Americans suffered their earliest-ever exit at a World Cup, losing to Sweden in the last 16 in Australia last August.

Veteran striker Alex Morgan echoed Kilgore's analysis.

"The whole world is continuing to raise its level," Morgan said. 

"Over the last five years or so you've just seen it. Ten years ago, 15 years ago, was way different with the scorelines than it is today.

"Teams are continuing to improve and evolve and can compete at the highest level. From the bottom to the top, there's just not that much of a gap anymore."

No one fears us

For some critics, though, the US team's recent struggles are as much a story of American decline as broader improvement in the global game.

Former US striker Carli Lloyd, a key member of the team that won back-to-back Olympic gold medals in 2008 and 2012 before claiming the 2015 and 2019 World Cups, believes the Americans are paying the price for complacency.

"Yes the whole world has caught up... but I actually hate when people say that because the USWNT started to regress at 2020 Olympics and have gone backwards," Lloyd wrote in a post on social media with the hashtag: "NoOneFearsTheUswntanymore."

"Teams used to lose the game before they played us because of fear and intimidation," Lloyd added. "As the complacency and lack of hunger crept in during 2020 it has given teams the confidence to know the US is beatable so that edge is lost."

Kilgore, who will make way for English coach Emma Hayes later this year, is backing her players to provide a riposte to Lloyd and other critics on Sunday.

"One thing that is always expected from us is a response," Kilgore said. "Generally that response is in-game and moment-by-moment. We're now tasked with doing a bit more. It's about getting right back to who we are, keeping it simple and executing."

The quarter-finals get under way on Saturday with Canada facing Costa Rica before Brazil face Argentina in a heavyweight South American showdown.

Costa Rica only made it through to the quarter-finals via a lottery held on Wednesday after the team finished with an identical record to Puerto Rico following the completion of the group phase.

That left CONCACAF officials scrambling to conduct a hastily arranged lottery in Houston, with Costa Rica's name being drawn first ahead of Puerto Rico to determine who would advance. 

Mexico, meanwhile, will fancy their chances of progressing against Paraguay on Sunday, before the US women take on Colombia in the final last-eight game.