Rossi scored twice and added assists on his side's other three goals as LAFC scored five unanswered after falling behind to continue their perfect start under coach Bob Bradley.
Latif Blessing, Benny Feilhaber and Carlos Vela also struck their first goals for the expansion side in a one-sided affair at Rio Tinto Stadium, which is usually one of the league's more formidable away venues.
That all came after Joao Plata briefly put the hosts ahead when he tucked in the rebound of a saved penalty, one awarded largely against run of play.
- 20' - RSL - Joao Plata Watch
- 30' - LAFC - Diego Rossi Watch
- 33' - LAFC - Latif Blessing Watch
- 48' - LAFC - Benny Feilhaber Watch
- 81' - LAFC - Diego Rossi Watch
- 86' - LAFC - Carlos Vela Watch
- THE BIG PICTURE: It's still early, but LAFC are already looking worthy of the hype with two away wins, a precious commodity in MLS. Remember, Houston, Kansas City, Philadelphia and New England all won only once away from home last season. The first two teams on that list still managed to qualify for the Audi 2017 MLS Cup Playoffs.
- MOMENT OF THE MATCH: While there was plenty of stylish combination play in the build to Blessing's go-ahead goal, the moments following proved even more crucial: Referee Baldomero Toledo and Video Assistant Referee (VAR) Juan Guzman Jr. appeared to hold a discussion, but declined a video review of the goal though it appeared Blessing and Steven Beitashour could have been ruled offside.
- MAN OF THE MATCH: Marco Urena was also excellent -- especially before halftime -- but how could it be anyone other than Rossi? The 20-year-old has now factored on every single goal in LAFC club history as he he lays some very early groundwork in the race for 2018 MLS Newcomer of the Year.