In this file photo, Juan Martin del Potro of Argentina celebrates his win over Sergiy Stakhovsky of Ukraine during their match at the Sydney International tennis tournament in Sydney, Tuesday, Jan. 13, 2015.
In this file photo, Juan Martin del Potro of Argentina celebrates his win over Sergiy Stakhovsky of Ukraine during their match at the Sydney International tennis tournament in Sydney, Tuesday, Jan. 13, 2015. Rick Rycroft AP
In this file photo, Juan Martin del Potro of Argentina celebrates his win over Sergiy Stakhovsky of Ukraine during their match at the Sydney International tennis tournament in Sydney, Tuesday, Jan. 13, 2015. Rick Rycroft AP