Third-seeded Jo-Wilfried Tsonga defeated Mikhail Youzhny of Russia 6-3, 6-2, and Feliciano Lopez of Spain outlasted Sam Querrey of the U.S. 4-6, 6-4, 6-4.
On the women's side, top-seeded Victoria Azarenka and second-seeded Maria Sharapova advanced. Azarenka topped Romina Oprandi 6-2, 6-0, and Sharapova was in charge of Angelique Kerber 6-0, 3-0 when the German retired with a right foot injury.
Djokovic had 12 aces and saved both break points he faced.
"The serve was great," he said. "It's one of the best serving matches I have had in my career, so that's a positive sign.
Djokovic was particularly pleased with serving four straight aces to win the sixth game of the second set at love. Fans went wild after the match when Djokovic signed his name on the TV camera lens in Mandarin.
Djokovic will take on Florian Mayer of Germany in the semifinal on Saturday. Mayer gave himself a big 29th birthday present with a 6-3, 6-4 win over Chinese wild card Zhang Ze.
Azarenka, the winner of four titles in seven finals this season, will meet Li Na., who moved closer to becoming the first Chinese finalist when she stopped Agnieszka Radwanska 6-4, 6-2.
Sharapova will play Marion Bartoli, who defeated Carla Suarez Navarro of Spain 6-0, 2-6, 6-4.
Sharapova said she was unaware of Kerber being injured before she surrendered the match. The Russian offered Kerber five chances to break serve, but held.
"I thought we played a high level of tennis the first set and a half, there were many games that went to deuce," Sharapova said. "I was surprised she called the trainer and even more so when she retired quickly after that."
Sharapova also seeks her eighth final appearance this year—she's won three titles, including her first French Open trophy.