Del Potro surprising himself with last-16 run

Sep 3, 2016; New York, NY, USA; Juan Martin del Potro of Argentina celebrates the win against David Ferrer of Spain on day six of the 2016 U.S. Open tennis tournament at USTA Billie Jean King National Tennis Center. Mandatory Credit: Anthony Gruppuso-USA TODAY Sports

NEW YORK (Reuters) - When former U.S. Open champion Juan Martin del Potro began his latest comeback in March he said he was playing for fun after three operations on his wrist.

Six months on, with an Olympic silver medal in the bag, the Argentine beat 11th seed David Ferrer of Spain 7-6 6-2 6-3 to reach the U.S. fourth round for the first time since 2012.