Emma Hayes hailed a “good start” to her reign as United States manager following a thumping 4-0 win over South Korea but conceded there was “lots of work to do”.

Doubles from Mallory Swanson and Tierna Davidson secured victory for former Chelsea boss Hayes in front of a sold-out crowd of 19,010 in Colorado.

Four-time Olympic champions the US are building towards this summer’s Paris Games, which begin late next month.

“I think you can see we’re building something,” Hayes was quoted as saying by ESPN.

“There’s lots of work to do. There’s lots of holes in our play, no question, but it was a good start. Everybody did what I asked of them.”

A fortnight on from guiding Chelsea to a fifth consecutive Women’s Super League title – and seventh of her 12-year tenure – Hayes took her first steps in international management.

Forward Swanson opened the scoring in the 34th minute at Dick’s Sporting Goods Park in Commerce City before defender Davidson headed home to double the advantage just four minutes later.

Colorado-born Swanson provided the assist for Davidson to double her tally early in the second period before rounding off a memorable debut for Hayes 16 minutes from time.

“In terms of what I had asked from the group, what we prepared for, the execution of that, we’ve made steps in the right direction,” added Hayes.

“I felt for the first 30 minutes, it was technical execution where we struggled. We scored in our first three chances, so we were efficient, we were clinical.”

The US face South Korea again on Tuesday at Allianz Field in St Paul, Minnesota.