Huerta opened the scoring and McCaskill, who assisted on the first goal, broke the game open with two goals after Sam Kerr's
penalty tied the score in the 23rd minute.
NWSL players scored five of the six goals as Alyssa Mautz's goal in the 68th minute drew Perth back to within one goal. Chloe Logarzo finished off the scoring in the 70th minute for Sydney FC, which won its first title since 2011.
Eight Americans in all started in the final -- Aubrey Bledsoe, Danielle Colaprico, Huerta and McCaskill for Sydney FC and Kathleen Naughton, Nikki Stanton, Rachel Hill and Mautz for Perth.
Colaprico has been called into the U.S. national team camp ahead of the SheBelieves Cup.