"Overall, my physicality is better this year," said Sock, who teamed with Melanie Oudin to win the mixed doubles championship at the 2011 U.S. Open and has been working with Andre Agassi's former trainer, Gil Reyes.
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"I just have to put in the work now," he said. "It's a process."
Citi Open tennis: Jack Sock among young Americans on rise →