Estrada, 26, was selected by the Sounders with the 11th overall pick in the 2010 MLS SuperDraft. He has started 18 of 41 appearances in his five seasons with Seattle, scoring five goals.
"David has been a fantastic member of our organization, both on and off the field, for the past five years," Sounders owner and general manager Adrian Hanauer said in a press release. "He has made great contributions to the team's performance and has been very involved in the community. We wish David the very best at D.C. United."
Estrada has made just one appearance in the 2014 MLS season, logging five minutes in a 1-0 victory at D.C. United on June 28. He also played 90 minutes and recorded one assist in a 5-0 win over PSA Elite in the U.S. Open Cup on June 18, and has started three MLS Reserve League matches.
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