Nishikori tames heat and big-serving Cilic
Kei Nishikori of Japan hits a forehand return to Marin Cilic of Croatia, during the Brisbane International tournament, on January 3, 2014
With temperatures approaching 37 degrees Celsius (99 degrees Fahrenheit), the second seeded Nishikori finished far stronger than the 198-centimetre-tall (six feet, six inch) Cilic, winning 6-4, 5-7, 6-2 in two hours, 37 minutes.
"It was hot -- it was tough conditions, especially playing a one hour (first) set and almost two hours and 40 minutes," he said. "It was not easy, but I'm happy to finish strong in third set.
"He was a little bit dropping his level (in the third) I think, yeah, I'm very happy today."
Nishikori, who broke Cilic's opening service game, said it was important that he made a mark early in the match.
"The tactics were to hit good returns and make whatever I could from his serve, especially his first serve," Nishikori said.
"I guess his first serve percentage was low today, so that helps too."
Nishikori now plays Australia's former world number one Lleyton Hewitt, who ended the run of Romanian qualifier Marius Copil 6-4, 6-2.
"He's always tough to play -- he doesn't miss much," Nishikori said of Hewitt.
"It's not easy (to play him) because he has decent serves and a good return and good backhand -- very solid on groundstrokes."