Murray breezes

Kukushkin, who was playing off the back of two five-setters in the Melbourne heat, threw in the towel early in the third set with a left hip flexor injury.

It was entirely comfortable for Murray, who will go into a last eight clash with Kei Nishikori relatively refreshed and in excellent nick, having recorded his ninth straight win.

Nishikori stunned sixth seed Jo-Wilfried Tsonga 2-6 6-2 6-1 3-6 6-3 in a gruelling clash later in the day on Hisense Arena, becoming the first Japanese man to reach the quarter-finals at Melbourne Park in the Open era.

A winner in Brisbane in the build-up to the first Grand Slam of the year, Murray took the match on Rod Laver Arena by the scruff of its neck from the outset and never looked like relinquishing control.

Murray's domination of baseline rallies, superior shot-making and court coverage made for a miserable day for his opponent, who failed to hold a single service game.

The two games Kukushkin did win were breaks of Murray's serve but otherwise the Scot was not troubled by the world number 92.

Murray's succession of breaks started in the very first game and despite dropping serve in the fourth game of the first set and the third of the second, he eased to a second win over Kukushkin this month, having met him in the first round in Brisbane.

Victory for the number four seed - finalist in Melbourne the last two years - sealed his progress to the quarter-finals for the third consecutive year and keeps alive his chances of breaking his Grand Slam duck under the guidance of new coach Ivan Lendl.

"I thought it was best he retired because it was pointless," Murray said. "The people probably weren't enjoying the match that much. I certainly wasn't because nothing was happening.

"Sometimes it's best just to stop."

Murray's next adversary Nishikori had to fight back from a set down against Tsonga, but eventually took advantage of a sub-par performance from the Frenchman to book his place in the last eight.

Nishikori follows in the footsteps of compatriots Ryosuki Nunoi and Jiro Satoh, who reached the same stage in 1932, 80 years ago.

The 22-year-old also becomes the first Japanese man to reach a Grand Slam quarter-final in the 17 years since Shuzo Matsuoka at Wimbledon in 1995.

Tsonga struggled to gain the upper hand on the energetic Nishikori, who broke the former Australian Open finalist's serve six times on his way to victory.

"Hopefully I can be like Li Na for the men," the 22-year-old said with a grin in reference to China's Li, who became Asia's first Grand Slam singles winner last year at the French Open.

"Honestly there's a lot of good players in Asia and I am happy to get to the top from Asia," added the 24th seed.

"This is the first (Grand Slam) quarter-final for me. (My) best result was the 2008 U.S. Open round of 16 (but) that was a couple years ago. So I feel I'm stepping up."