Del Potro improved to 20-5 this year with his straight-set dumping of the Swede, 6-3, 6-2, and now moves on to face American Mardy Fish.
The 14th-seeded Fish gained the fourth round for the second straight year, this time by earning a 6-4, 6-3 decision over 17th-seeded Frenchman Richard Gasquet.
Also notching a win Sunday was No. 6 David Ferrer of Spain, who dispatched India's Somdev Devvarman 6-4, 6-2. Ferrer, the winner of this year's Auckland and Acapulco events, now faces countryman Marcel Granollers, who defeated 23rd-seeded Frenchman Michael Llodra 7-5, 3-6, 7-5.
South Africa's Kevin Anderson and John Isner of the United States also registered wins Sunday.
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