Juan Martin Del Potro advanced to the quarter-finals of the Open 13 when Nikolay Davydenko of Russia retired with an apparent foot injury on Thursday with the match level at one set apiece in Marseille.

The fourth-seeded Argentine lost the opening set 7-6 (6) but took the second 6-4 when Davydenko said he couldn’t play anymore.

The Russian put Del Potro under pressure in the first set by winning 10 of 12 points at the net. He saved four set points and hit 22 winners to 14 for the 2009 US Open champion.

Del Potro fought back in the second set, breaking to make it 4-3 when Davydenko double-faulted. He served his 16th ace to close it out.

Del Potro paid tribute to the victims of Wednesday’s train crash in Buenos Aires by wearing a black ribbon on his T-shirt.

He will next 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 now reached the quarter-finals four times this season.

Michael Llodra of France also advanced by upsetting sixth-seeded Alexandr Dolgopolov of Ukraine 6-4 5-7 7-6 (5).

Llodra had 19 aces, and the 2010 champion won four straight points to take a 5-2 lead in the deciding tiebreaker.