An ailing Novak Djokovic said Saturday every moment counted now that he was in the "last stage" of his career, after battling past Grigor Dimitrov and into the Australian Open last 16.

The Serb came through a titanic 77-minute first set before taming the Bulgarian 7-6 (9/7), 6-3, 6-4 on Rod Laver Arena, needing treatment twice on his troublesome hamstring.

He will face home hope Alex de Minaur for a place in the quarter-finals after the 22nd seed equalled his best result at the tournament by defeating Frenchman Benjamin Bonzi in three sets.

Djokovic's gutsy win inched him nearer to a 10th Australian Open title and record-tying 22 Grand Slam crowns.

Winning once again in Melbourne would also return him to world number one for the first time since June.

Now 35, Djokovic said he was savoring each tournament more.

"Every season counts I guess now, when you come to the last stage, the last quarter, of your career," he said.

"Obviously you start appreciating and valuing each tournament more because you might not have a lot left in the tank.

"I've been truly fortunate to do what I love, I love the sport, I love competing. It's been almost 20 years now of professional sport. I can't be more grateful than I am."

Victory put Djokovic into the last 16 for a 15th time but he was made to work for it, especially with his left hamstring troubling him.

"Every point, every game mattered," he said.

"Obviously I didn't know how I'm going to feel physically, it was going up and down," he said.

"It was an incredible battle, three sets over three hours."

Djokovic aggravated his hamstring during his run to a 92nd title at the Adelaide International this month and has been struggling with it since.