Defending champion Del Potro beat Paul-Henri Mathieu of France 6-2, 7-6 (2) to reach the ATP World Tennis quarter-finals on Thursday.
The Argentine had to save two set-points on serve at 5-6 in the second set to move on to next play Latvian Ernests Gulbis, who beat eighth-seed Grigor Dimitrov of Bulgaria 6-4, 7-6, reported Xinhua.
Second-seeded Andy Murray eliminated Austrian qualifier Dominic Thiem 6-4, 3-6, 6-3.
They were evenly matched in the first two sets, with Thiem saving three break points to take the second. But Murray asserted himself in the third, in an exciting match which lasted 2 hours, 21 minutes.
Del Potro was troubled with wrist injury, saying "still feeling pain in his left wrist".
"Sometimes I get frustrated. It's not easy when I want to close the point and hit hard but I have to hit slices. I have done this for the past month on the tour and I have to deal with it. If the pain goes away, I will start to hit the backhand harder again."
Murray faces Marin Cilic in the quarter-finals after Cilic upset fifth-seed Jo-Wilfried Tsonga 6-4, 6-4.
Third-seeded Tomas Berdych beat Nicolas Mahut of France 6-4, 6-3 and will meet Wimbledon semi-finalist Jerzy Janowicz Friday.
Fourth-seeded Richard Gasquet was knocked out by Philipp Kohlschreiber 7-5, 7-5, and the German will face Dutch wild card Igor Sijsling.