The Galaxy (10-5-7) pulled within two points of Western Conference leaders FC Dallas, Real Salt Lake and Seattle while winning back-to-back games for the fifth time this season.
The fifth-place Whitecaps (7-5-12), who watched their six-game unbeaten streak end, lost for just the third time since back-to-back showdowns with LA in mid-April and remain nine points off the Western lead and seven in back of the Galaxy.
Vancouver was without its two first-choice holding midfielders -- Matias Laba is suspended and Gershon Koffie injured -- but Pedro Morales returned to his spot behind striker Darren Mattocks. A.J. DeLaGarza returned to left back for the Galaxy, with Todd Dunivant back on the bench, and Baggio Husidic got the call in midfield instead of Stefan Ishizaki, who had a minor toe injury.
Mauro Rosales, whom the Whitecaps acquired Thursday in a trade with Chivas USA, made his club debut at the start of the second half. Center back Johnny Leveron was red-carded in the 90th minute after a harsh tackle near midfield on Alan Gordon.
LA, which had conceded the first goal in their past four and five of their past six games, was ahead from the start. Donovan provided a fourth-minute lead with his sixth goal of the season, the fourth assisted by Keane.
Marcelo Sarvas chipped a ball from the right flank toward the penalty spot in Vancouver’s box, and Andy O’Brien beat Gyasi Zardes to the ball, nodding it out toward the top of the box. Keane stepped up to half-volley what appeared to be a shot, but the ball instead rolled through traffic to the far post, where Donovan placed it into the goal’s ceiling.