The Serbian was detained for just under an hour as he won 6-1 6-2 with a performance which was simply too strong for Melzer.
Next up for Djokovic is Germany's Florian Mayer, who beat home favourite Zhang Ze 6-3 6-4.
The other last-four tie pits Feliciano Lopez against Jo-Wilfried Tsonga.
Lopez edged a tight match against American Sam Querrey by breaking in the final game of the deciding set to complete a 4-6 6-4 6-4 triumph.
Tsonga had a far easier time, beating Mikhail Youzhny 6-3 6-2, but was still underwhelmed by his display.
"I'm a bit disappointed with my game on the baseline; I didn't play really good tennis," admitted Tsonga.
"Today it was not brilliant, but was solid enough to win it today. I served well and that's it."
In the women's event, world number one Victoria Azarenka advanced to the last four by thrashing Romina Oprandi 6-2 6-0.
"It's never easy to go on court and win the match even though the score is like this," Azarenka said.
"Sometimes it's important to stay tough and have that concentration to make sure that you can win every ball and every point."
The Belarusian will play Marion Bartoli for a place in the final following the Frenchwoman's 6-0 2-6 6-4 win over Spain's Carlo Suarez Navarro.
Chinese favourite Li Na cruised into a semi-final meeting with Maria Sharapova after beating defending champions Agnieszka Radwanska 6-4 6-2.
Sharapova went through when her quarter-final opponent Angelique Kerber retired when 6-0 3-0 down.
Kerber appeared to have a foot injury when she offered her hand midway through the second set.
"I actually didn't see much of her injury," Sharapova said.
"I was surprised she called the trainer and even more so when she retired quickly after that. I thought we played a high level of tennis the first set and a half, and even though the scoreline was 6-0 3-0, there were many games that went to deuce."