Keane's tally in the 78th minute, off a headed pass from Hector Jimenez, earned a point for the playoff-bound Galaxy (15-11-8), which finished in third place in the Western Conference.
The two-time defending MLS champions will face Real Salt Lake in the West semifinals.
U.S. international Clint Dempsey scored his first goal in a Sounders uniform for fourth-place Seattle (15-12-7), which enters the post-season on a seven-game winless streak.
The Sounders will play Colorado in the West knockout round.
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