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Rubén Ramírez Hidalgo was the defending champion , but lost to Diego Sebastián Schwartzman in the first round .
 Rubén Ramírez Hidalgo, Diego Sebastián Schwartzman
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Rubén Ramírez Hidalgo, Diego Sebastián Schwartzman