Djokovic got past 16th-seeded Alexandr Dolgopolov 2-6, 6-1, 6-4. Dolgopolov cashed in both of his break-point opportunities in the first set but Djokovic didn't drop his serve after that.
He ended up winning 70 percent of the points on serve, losing 20 points over 13 games.
The match was tied 4-4 in the third set when Djokovic finished off his third break of the day. He then held serve for the win.
Second-seeded Rafael Nadal claimed his 39th consecutive match win at the Monte Carlo Masters with a 6-1, 6-1 rout of Mikhail Kukushkin in 60 minutes. Nadal won nearly three-quarters of the points in the match and lost only six points in seven service games.
Nadal is seeking an eighth consecutive championship at the event.
No. 3-seeded Andy Murray advanced when Julien Benneteau retired after falling and injuring his wrist and ankle when Murray was up 6-5 in the first set. Fourth-seeded Jo-Wilfried Tsonga moved to the quarterfinals with a 7-6 (9-7), 6-2 decision over 13th-seeded Fernando Verdasco.
Stanislaw Wawrinka knocked off eighth-seeded Nicolas Almagro 6-3, 6-3 and Gilles Simon, the No. 9 seed, pulled off a minor upset by beating seventh-seeded Janko Tipsarevic 6-0, 4-6, 6-1. Although Simon was the lower seed, he is 4-0 against Tipsarevic.
Also Thursday, sixth-seeded Tomas Berdych rallied for a 2-6, 6-2, 6-4 win over No. 12 Kei Nishikori and Robin Haase dispatched Thomaz Bellucci 6-2, 6-3.
Friday's quarterfinals have Djokovic going against Haase and Murray playing Berdych in one half of the draw while Nadal faces Wawrinka and Tsonga plays Simon in the other.