Cristian Arango scored for LAFC (4-1-1), which had won three straight games by two-goal margins. It was an especially frustrating outing for forward Carlos Vela, who could not match Chicharito in the first meeting of the former Mexican internationals in Major League Soccer.
Latif Blessing looked to have tied it at 2 in the seventh minute of second-half stoppage time when he put the ball in after a frantic scramble in front of goal, but referee Chris Penso waived it off after video review showed Mamadou Fall was offsides in the buildup.
Coulibaly got his first goal in 24 games for the Galaxy in the 31st minute to make it 2-0. Grandsir was able to chest down Raheem Edwards' pass following a short corner before spinning around to send the ball through the box where Coubali coolly finished.