The world number one was in devastating form, conceding just three aces in a masterclass performance to reach the semi-finals in Beijing.
The Serbian is chasing his sixth title in Beijing and his seventh this year, which already includes the Australian Open, Wimbledon and US Open.
"Today was a great match," said Djokovic. "Obviously the fact that he served that high of a first percentage of serves in and I managed to break him twice says enough about the quality of the return that I had today. That was the key to winning the match.
Karlovic sets new all-time aces record as Djokovic reaches China Open last eight
"Conditions didn't help him, didn't help his serve, even though he was serving around 200 average. But I was managing to pick up balls from each corner on the return. I was feeling like I can get a lot of balls back in play and make him move, which was one of the intentions tactically in order to be successful today."
Djokovic's next opponent is Spain's David Ferrer, who won the Malaysian Open last week. Ferrer eased into the semi-finals with a 6-3 6-1 victory over Taiwan's Lu Yen-hsun.
Rafael Nadal had a much harder time in his quarter-final with American Jack Sock, before prevailing 3-6 6-4 6-3.
The Spaniard is still struggling to get back to his best but said he was pleased with the way he fought back.
"Obviously I finished the match playing better than what I started. This year I lost a lot of matches when I had an advantage," Nadal said.
"So to have the chance to win a match when I start losing is important for me."
Nadal will face Fabio Fognini in the semi-finals after the Italian beat Pablo Cuevas 6-1 2-6 6-2. Nadal has lost three of his last four matches against Fognini, including at the U.S. Open when he blew a two-set lead in the third round.
"When you play against a great player, especially if you don't play to your best, your chances are lower," Nadal said.
"If I am able to play my best tomorrow, I am going to have my chances. If not, it is going to be tough. It's simple. Sport is simple. The winner is the player who plays better. Fognini played better in the three matches that he beat me."
In the women's draw, Wimbledon finalist Garbine Muguruza beat Bethanie Mattek-Sands of the U.S. 6-1 7-5 to ease into the semi-finals, joining Ana Ivanovic, Agnieszka Radwanska and Timea Bacsinszky.
Nadal pushed by Pospisil before reaching China Open quarters, but Berdych out
Nadal made to work to win Beijing opener, Djokovic cruises
Share this article