Djokovic, the top seed in the event, got by Gael Monfils 6-7 (4-7), 6-2, 6-4 in a 2-hour, 22-minute battle. Djokovic has never lost to Monfils but the French player made Friday's match interesting with a strong first set.
Monfils fired off six aces in the set and had a pair of breaks to get to a tiebreaker. But Djokovic allowed Monfils just one break chance the rest of the way in winning for the 16th time in his last 17 matches overall. He is 9-0 in his career against Monfils.
World No. 1 Rafale Nadal broke open a tight match against ninth-seeded Stanislas Wawrinka, winning 7-6 (12-10), 6-1. Nadal took 70 percent of the points in the second set after he won only three more points that Wawrinka in the first set.
Nadal moved to 11-0 all-time against Wawrinka, who is yet to win a set from Nadal.
No. 6-seeded Juan Martin del Potro moved within one match victory of qualifying for the ATP World Tour Finals after he beat 15th-seeded Nicolas Almagro 6-3, 6-3. Del Potro lost only 12 points in nine games serving.
The fourth quarterfinal went to No. 6-seeed Jo-Wilfried Tsonga with a 6-2, 6-3 victory over Florian Mayer. Tsonga saved all four of the break points Mayer managed.
Djokovic draws Tsonga in Saturday's semifinals. Djokovic has a six-match winning streak against Tsonga, extending his series advantage to 10-5. Nadal is 8-3 versus del Potro but they had a close three-set match this year at Indian Wells, Calif., in their most recent meeting.