The Rapids forward tallied a landmark strike against LA, but his former club came back to win and take all three points.
The 33-year-old scored his second of the season in the 17th minute to send Pablo Mastroeni's side up 2-0 against the Galaxy, but Robbie Keane scored almost immediately after, and although Marc Burch restored the two-goal lead on the half-hour mark with an impressive free kick, LA scored three without reply after the interval to win a thrilling encounter.
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The result is a difficult one for Colorado, which could have re-taken a playoff spot with a big enough margin of victory and looked at halftime to at least have done enough for the win. The Rapids now sit in seventh place in the West, with Vancouver occupying the last playoff berth, three points ahead and holding two games in hand.
The 100-goal club is sparsely populated, with Buddle joining former teammate Landon Donovan (who scored his league-record 139th career goal in the 80th minute), Jeff Cunningham, Jaime Moreno, Ante Razov, Jason Kreis, Dwayne De Rosario and Taylor Twellman.
Buddle joined MLS in 2001 when he was drafted by the columbus Crew, and also played with the New York Red Bulls and had a brief stint with Toronto FC. Before being traded to Colorado, Buddle played two stints with LA, spending two years with German club Ingolstadt 04 in between.
The striker has also made 11 appearances for the United States men's national team, scoring three goals, and was a part of the 2010 World Cup squad.