The American hasn’t dropped a set and has been broken only once while reaching the quarterfinals.
Serbia’s Viktor Troicki took del Potro to three sets before fading. The Argentinian improved to 6-0 career against Troicki with a 7-6 (2), 2-6, 6-1 win.
On the women’s side, top-seeded Agnieszka Radwanska overcame an unexpected challenge from wild-card Sloane Stephens before winning 6-1, 4-6, 6-4. Radwanska, who lost to Serena Williams in the Wimbledon final, reached the tournament’s quarterfinal for the first time in three appearances.
Germany’s Angelique Kerber advanced with a 6-4, 7-6 (5) win over qualifier Andrea Hlavackova of the Czech Republic.
AP freelance writer Mark Schmetzer contributed to this report.
By Elaine Donnelly
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