Los Angeles FC hands Seattle first loss of season.
Kaye cut back to evade a defender near midfield, took a couple dribbles and played a through ball to Vela, who split two defenders at the top of the box before side-netting a left-footer from near the spot to open the scoring in 12th minute.
Eduard Atuesta ran onto a pass by Seattle's Nicolás Lodeiro that Kaye deflected, hesitated at the top of the box to evade a sliding defender and then ripped a right-footer inside the far post to make it 2-0 in the 39th.
Seattle's Harry Shipp scored his first goal of the season in the 51st minute, but Vela took a through pass from Atuesta, evaded a charging goalkeeper Stefan Frei and then put away the empty-netter to give LAFC (7-1-1) a 3-1 lead in the 55th. Christian Ramirez back-heeled a pass to Kaye near the top of the box, who rolled it back to Ramirez for the finish from near the spot to cap the scoring in the 61st minute.
Seattle (5-1-1) had its 11-game regular-season unbeaten streak snapped.
NYCFC (1-1-5) snapped an eight-game winless streak, dating to the 2018 MLS playoffs.
Sean Johnson had three saves in his third shutout of the season for NYCFC.
D.C. United (4-2-2) was outshot 18-10.