Galaxy clinch playoffs berth for first time since 2019, Philadelphia thrashed by Charlotte after Rios quartet
Douglas Costa converted the 68th-minute penalty won by Hernandez, after Riqui Puig had his 17th-minute spotkick saved by RSL goalkeeper Zac MacMath.
RSL had gone ahead in the 25th minute from Sergio Cordova's header, but were left to lament Justen Glad failing to convert two late golden opportunities from headers, denting their playoff hopes and extending their winless run to five games.
Ex-Manchester United forward Hernandez earned Galaxy's reprieve after review when bundled over by Marcelo Silva inside the box, with Costa sending MacMath the wrong way.
The draw was enough for the Galaxy, who are perched fourth in the Western Conference with 47 points from 33 games, with RSL sitting eighth, just outside the playoff spots, with 44 points from 33 games.
Derrick Etienne scored two late goals against his former side to earn Columbus Crew a 2-1 win over New York Red Bulls, who suffered their third defeat in four games.
Etienne equalized Franuel Amaya's 53rd-minute thunderbolt with an 89th-minute strike on the turn, before grabbing a 93rd-minute winner by lashing home a rebound.
Philadelphia Union handed the initiative to LAFC in the Supporters' Shield hunt after being thrashed 4-0 by Charlotte, for whom Daniel Rios netted four goals, achieving a franchise-first hat-trick.
The defeat means Philadelphia have failed to win in their past two games, leaving them on 64 points from 33 games, while LAFC have the same number of points with two games to play, starting with Portland Timbers on Sunday.
Donovan Pines scored an own goal and was red carded as DC United lost 1-0 to Montreal, who closed within two points of Eastern Conference leaders Philadelphia with one game to play.
Sergio Santos was sent off amid a late scuffle as Cincinnati missed a chance to practically clinch a playoff spot with a 3-2 home loss to Chicago Fire. Cincinnati fought back from 3-0 down after Jhon Duran's double for Chicago.
Minnesota United's winless run extended to six games after going down 2-0 to San Jose Earthquakes, leaving them in a precarious position in the race to qualify for the Western Conference playoffs.
Vancouver Whitecaps capitalized on Minnesota and RSL's results and beat Austin 2-0 to keep alive their playoff hopes with their third straight victory. The Whitecaps are ninth in the west with 43 points with one game to play, with seventh-placed Minnesota on 45 and RSL on 44.
Josef Martinez scored a spectacular scissor-kick goal but Atlanta United went down 2-1 to New England, while playoff-bound Dallas lost 1-0 at Colorado Rapids.