Sisniega made his professional debut on 11 June 2019, starting in a 3–0 win over Real Salt Lake in a Lamar Hunt US Open Cup fixture. On 20 June 2019, with Tyler Miller away at the 2019 Gold Cup, Sisniega made eight saves to help Los Angeles win 3–1 over San Jose Earthquakes in the Round of 16 of the US Open Cup. On 3 July 2019, in his second MLS appearance, Sisniega made several key saves to help his team in a 5–1 away win at Sporting Kansas City, including an 82nd minute penalty save on Daniel Salloi.