Emma Hayes got her international coaching career off to a flying start on Saturday as the United States defeated South Korea 4-0 in a friendly in Colorado.

Mallory Swanson and Tierna Davidson scored two goals apiece to give Hayes a resounding victory in her first game in charge of the American women since her appointment was announced in November last year.

The 47-year-old former Chelsea boss was named to the US job in the wake of the USA's early exit at last year's Women's World Cup, and has been tasked with reviving the fortunes of the four-time world champions.

Hayes couldn't have hoped for a smoother start to her reign as a confident US line-up dismantled the Koreans in bright sunshine at a packed Dick's Sporting Goods Park in suburban Denver.

"We were controlled in what we did in the first half, we struck to the structures and the coaching," Hayes said. "Everybody did what I asked of them.

"It's really nice to feel like I've got the trust and the belief in the group to be able to play football. And while the American DNA and mentality is one that we don't want to lose, being able to play the way that we are is really exciting."

Hayes inherited a US squad grappling with controversy in April after anti-LGBTQ social media posts by midfielder Korbin Albert came to light. Albert was handed her first minutes under Hayes on Saturday after appearing as a substitute.

The English coach said after Saturday's game, which saw the US team wearing shirts emblazoned with rainbow-colored numbers to mark the start of Pride month, that she wanted to build a tolerant team culture.

"We want an environment which is tolerant and respectful and even though there's difference, it's important for us that we live up to the values and everything this team is about," Hayes said. 

"This week it's been about football, football, football. As we say in England, it's been a lovely week."

The Americans took the lead through a well-worked goal from Swanson in the 34th minute.

Naomi Girma's pass from midfield found Sophia Smith on the edge of the area, and the US striker timed her pass to perfection to send in Swanson, who tucked away a confident finish.

Central defender Davidson made it 2-0 four minutes later, her high looping header from a Catarina Macario corner dropping into the net with South Korean goalkeeper Kim Jung-mi stranded.

Davidson grabbed her second goal three minutes into the second half, aiming a downward bouncing header back across goal and into the net after being picked out by Swanson's cross.

Next it was Swanson's turn to complete her double, latching onto a deft pass from substitute Rose Lavelle to rifle her finish past Korean goalkeeper Kim.

The two teams will play again in a second friendly in Minneapolis on Tuesday, giving Hayes a final opportunity to run the rule over her players before naming the US squad for the Paris Olympics.