8420
Results of first round matches on Tuesday in the U.S. Open tennis championships at the National Tennis Centre ( prefix denotes seeding ) :
 U.S. Open, National Tennis Centre
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, else, organization, person 
Text: {0} 
Answer:
 U.S. Open, National Tennis Centre