The Sounders backstop earns the honor in his final professional season.
In his final professional season, Keller led all MLS goalkeepers with 18 wins and posted a 1.09 goals against average and nine shutouts. His 75.9 save percentage was second in MLS among those with 20 or more games played
"I'm proud that I was able to perform at the level in my final year that I hoped to achieve," Keller said.
"Anytime you receive an award it's always nice that someone has thought of you in that regard. I have never played the game for the awards but it's nice to be recognized by your peers."
The 41-year-old was named to the 2011 MLS Best XI in the final season of his 20-year professional career, and was named an MLS All-Star in each of his three seasons in the league.
"Kasey had a superb season, finishing his career at such a high level is a reflection of his professionalism and high standards," said Sounders FC coach Sigi Schmid. "The game will miss him and we are proud that he was a Seattle Sounder."
The Philadelphia Union's Faryd Mondragon finished second in the voting, followed by Kevin Hartman of FC Dallas, then Nick Rimando of Real Salt Lake and Dan Kennedy of Chivas USA.
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