Djokovic cut a frustrated figure as he was made to work hard for a 6-4 7-5 7-5 win on Rod Laver Arena, the world number one’s mood perhaps not improved by knowing he faces more of the same big serving from Milos Raonic in the last eight.
“It gets easier and easier with opponents and their serves,” Djokovic joked in an on-court interview with four-time grand slam winner Jim Courier. “Milos has been playing the tennis of his life in the last 15 months. We are good friends and practice a lot together. He is one of the new generation of stars.”
A single break of serve was enough for Djokovic to win each set against Muller, although the top seed had to save four break points midway through the third set and appeared unhappy with the lack of grip from his footwear on several occasions.
“Not playing Gilles before it was tricky coming in,” Djokovic added. “I did not know what to expect. I knew he had struggled with injuries recently but he beat some top players here and deserved a lot of respect.
“I was fortunate to serve very well in important moments in the third set. It was very hard to read his serve and he has a lot of variety in his game.”
Roger Federer was surprisingly the only top seed not to advance to the last eight, the 17-time grand slam winner having lost in the third round, with fourth seed Stan Wawrinka, fifth seed Kei Nishikori and eighth seed Raonic all winning on Monday.