Every player from Republic of Ireland international Denise O'Sullivan's North Carolina Courage and Portland Thorns took a knee during the U.S. national anthem and wore t-shirts with the slogan "Black Lives Matter" prior to their National Women's Soccer League match yesterday.

In a joint statement, the players said they did so to protest racial injustice, police brutality and systemic racism against Black people and other people of color in America.

"We love our country and we have taken this opportunity to hold it to a higher standard," the players said.

"It is our duty to demand that the liberties and freedoms this nation was founded upon are extended to everyone."

The protest was popularized by San Francisco 49ers quarterback Colin Kaepernick in 2016 and the gesture has again gained momentum following the death of George Floyd, a Black man who died in police custody in Minneapolis last month.

Earlier this month, the US Soccer Federation dropped its requirement that players stand during the US anthem, drawing the ire of president Donald Trump. Former US manager Bruce Arena has questioned the relevance of playing the anthem for non-international games.

Ballon d'Or winner Megan Rapinoe of OL Reign tweeted in support for yesterday's protest.

"You love to see these women using their voice, demanding better for America, and for Black people and people of color," Rapinoe said.

Saturday's match in suburban Salt Lake City, Utah, marked the first time a major North American league has returned to action since the start of the COVID-19 outbreak, which upended the sports calendar in March.

The favored Courage prevailed 2-1 over the Thorns after Lynn Williams headed in the game winner in stoppage time to kick off the month-long Challenge Cup tournament.

Later on Saturday, the Washington Spirit shared an image of most of their team kneeling before their game against the Chicago Red Stars.

Spirit head coach Richie Burke said before the match that he would kneel for the anthem "to recognize the struggle players, friends, team mates and former opponents have had with racism."

"I'm grateful for everything this country has given me, but I feel the need to support the Black Lives Matter movement because I know this privilege isn't the same for everyone," he said.

Goals from Ashley Hatch and Rose Lavelle helped Washington beat Chicago 2-1.