MARSEILLE, France (AP) -- Juan Martin Del Potro advanced to the quarterfinals of the Open 13 on Thursday when Nikolay Davydenko retired because of a foot injury.
The Argentine lost the opening set 7-6 (6) and won the second 6-4 before Davydenko said he couldn't play.
He'll face Richard Gasquet, who cruised past Igor Kunitsyn of Russia 6-3, 6-2.
The fifth-seeded Frenchman broke Kunitsyn's serve three times and saved all six break points he faced.
Gasquet has reached the quarterfinals four times this season.
Michael Llodra of France edged Alexandr Dolgopolov of Ukraine 6-4, 5-7, 7-6 (5) to reach the quarterfinals. Llodra had 19 aces, and the 2010 champion won four straight points to take a 5-2 lead in the tiebreaker.
Del Potro paid tribute to the victims of Wednesday's commuter train crash in Buenos Aires by wearing a black ribbon on his T-shirt. Fifty people died when the train crashed at a downtown station.