Rafael Nadal smiles during a press conference at Zayed Sports City in Abu Dhabi on Thursday ahead of the Mubadala World Tennis Championship. Marwan Naamani / AFP
Novak Djokovic signs autographs at Zayed Sports City on Thursday for the Mubadala World Tennis Championship in Abu Dhabi. Ravindranath K / The National
Rafael Nadal, left, and Stan Wawrinka arrive on Thursday at the Beach Rotana in Abu Dhabi for an appearance ahead of the Mubadala World Tennis Championship. Ali Haider / EPA
Andy Murray practices on Thursday at the Zayed Sports City tennis centre ahead of the Mubadala World Tennis Championship in Abu Dhabi. Ali Haider / EPA
Stan Wawrinka plays a shot during his opening match on Thursday night at the Mubadala World Tennis Championship in Abu Dhabi. Wawrinka defeated Nicolas Almagro. Kamran Jebreili / AP
Nicolas Almagro returns a shot during his loss to Stan Wawrinka in the Mubadala World Tennis Championship in Abu Dhabi on Thursday night. Martin Dokoupil / Reuters
Rafael Nadal poses with fans at Zayed Sports City in Abu Dhabi on Thursday ahead of the Mubadala World Tennis Championship. Kamran Jebreili / AP
Novak Djokovic responds to a question during his press conference on Thursday ahead of the Mubadala World Tennis Championship in Abu Dhabi. Ali Haider / EPA
Andy Murray prepares to play a shot against Feliciano Lopez in his win on Thursday night at the Mubadala World Tennis Championship in Abu Dhabi. Francois Nel / Getty Images
Feliciano Lopez plays a shot at the net during his loss to Andy Murray on Thursday night at the Mubadala World Tennis Championship in Abu Dhabi. Ali Haider / EPA
From left to right, Feliciano Lopez, Stan Wawrinka, Rafael Nadal, Novak Djokovic, Andy Murray and Nicolas Almagro pose during a photo shoot in Abu Dhabi on Thursday. AFP Photo / Mubadala World Tennis Championship