Possible Clues:

• Org. for Nadal and Djokovic
• Org. for Federer and Nadal
• Org. for paid tennis players
• Org. that publishes weekly player rankings
• Netmen's gp
• Pro tennis org
• Court org
• Court sport org
• Molecule that carries energy: Abbr
• Org. for Agassi and Roddick