Despite an impressive performance Del Potro played down his chances of landing his biggest title since winning the US Open in 2009, also against Federer.
“I don’t know who is the favorite,” Del Potro, a finalist in London three years ago, said. “Djokovic, Murray or Federer can win the tournament. I can tell you I’m the No. 4 for sure.”
In doubles play, top seeds and three-time former champions Bob and Mike Bryan lost to India’s Leander Paes and Radek Stepanek, meaning the US players missed out on the semi-finals.
Paes and Stepanek won a match tiebreak 10-7 and will face Mahesh Bhupathi and Rohan Bopanna in the semi-finals. In the other semi-final, Britain’s Jonathan Marray and Dane Frederik Nielson will play Spaniards Marcel Granollers and Marc Lopez.